npm run devが上手く行かない

#背景

Laravelとvue.jsを使ってチャットのwebサービスを作っていました。
こちらのサイトを参考にしております。
https://dev.to/mezie/how-to-build-a-laravel-chat-app-with-pusher-2e2o

laravel-echoとpusherを使ったリアルタイムチャットです。

eventの作成など一通り終わった後で、Laravel Mixを使ってJavaScriptファイルをコンパイルしようとした所で以下のようなエラーが出ました。

エラーコードを読んだ感じだとコンパイルに失敗していて./resources/sass/app.scssにエラーがあるとの事なのですが、特にapp.scssは弄った覚えがないです。

##エラーコード

xxxMacBook:laravel_chat xxx$ npm run dev

> @ dev /Users/xxx/Desktop/laravel_chat
> npm run development


> @ development /Users/xxx/Desktop/laravel_chat
> cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js

98% after emitting SizeLimitsPlugin

 ERROR  Failed to compile with 2 errors                                                                                 16:01:00

 error  in ./resources/sass/app.scss

Module build failed (from ./node_modules/css-loader/index.js):
ModuleBuildError: Module build failed (from ./node_modules/sass-loader/lib/loader.js):

@import "utilities/clearfix";
       ^
      Can't find stylesheet to import.
  ╷
4 │ @import "utilities/clearfix";
  │         ^^^^^^^^^^^^^^^^^^^^
  ╵
  node_modules/bootstrap/scss/_utilities.scss 4:9  @import
  node_modules/bootstrap/scss/bootstrap.scss 43:9  @import
  stdin 8:9                                        root stylesheet
      in 

 error  in ./resources/sass/app.scss

Module build failed (from ./node_modules/sass-loader/lib/loader.js):

@import "utilities/clearfix";
       ^
      Can't find stylesheet to import.
  ╷
4 │ @import "utilities/clearfix";
  │         ^^^^^^^^^^^^^^^^^^^^
  ╵
  node_modules/bootstrap/scss/_utilities.scss 4:9  @import
  node_modules/bootstrap/scss/bootstrap.scss 43:9  @import
  stdin 8:9                                        root stylesheet
      in /Users/xxx/Desktop/laravel_chat/node_modules/bootstrap/scss/_utilities.scss (line 4, column 9)

 @ ./resources/sass/app.scss 2:14-255

     Asset      Size   Chunks             Chunk Names
/js/app.js  1.68 MiB  /js/app  [emitted]  /js/app

ERROR in ./resources/sass/app.scss
Module build failed (from ./node_modules/css-loader/index.js):
ModuleBuildError: Module build failed (from ./node_modules/sass-loader/lib/loader.js):

@import "utilities/clearfix";
       ^
      Can't find stylesheet to import.
  ╷
4 │ @import "utilities/clearfix";
  │         ^^^^^^^^^^^^^^^^^^^^
  ╵
  node_modules/bootstrap/scss/_utilities.scss 4:9  @import
  node_modules/bootstrap/scss/bootstrap.scss 43:9  @import
  stdin 8:9                                        root stylesheet

 ERROR in ./resources/sass/app.scss (./node_modules/css-loader??ref--5-2!./node_modules/postcss-loader/src??postcss0!./node_modules/resolve-url-loader??ref--5-4!./node_modules/sass-loader/lib/loader.js??ref--5-5!./resources/sass/app.scss)
Module build failed (from ./node_modules/sass-loader/lib/loader.js):

@import "utilities/clearfix";
       ^
      Can't find stylesheet to import.
  ╷
4 │ @import "utilities/clearfix";
  │         ^^^^^^^^^^^^^^^^^^^^
  ╵
  node_modules/bootstrap/scss/_utilities.scss 4:9  @import
  node_modules/bootstrap/scss/bootstrap.scss 43:9  @import
  stdin 8:9                                        root stylesheet
      in /Users/xx/Desktop/laravel_chat/node_modules/bootstrap/scss/_utilities.scss (line 4, column 9)
 @ ./resources/sass/app.scss 2:14-255
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @ development: `cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the @ development script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/xxx/.npm/_logs/2019-08-04T07_01_02_384Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @ dev: `npm run development`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the @ dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/xxx/.npm/_logs/2019-08-04T07_01_02_409Z-debug.log

##app.scss

// Fonts
@import url('https://fonts.googleapis.com/css?family=Nunito');

// Variables
@import 'variables';

// Bootstrap
@import '~bootstrap/scss/bootstrap';

##app.js

/**
 * First we will load all of this project's JavaScript dependencies which
 * includes Vue and other libraries. It is a great starting point when
 * building robust, powerful web applications using Vue and Laravel.
 */

require('./bootstrap');

window.Vue = require('vue');

/**
 * The following block of code may be used to automatically register your
 * Vue components. It will recursively scan this directory for the Vue
 * components and automatically register them with their "basename".
 *
 * Eg. ./components/ExampleComponent.vue -> <example-component></example-component>
 */

// const files = require.context('./', true, /.vue$/i);
// files.keys().map(key => Vue.component(key.split('/').pop().split('.')[0], files(key).default));

Vue.component('chat-messages', require('./components/ChatMessages.vue'));
Vue.component('chat-form', require('./components/ChatForm.vue'));

/**
 * Next, we will create a fresh Vue application instance and attach it to
 * the page. Then, you may begin adding components to this application
 * or customize the JavaScript scaffolding to fit your unique needs.
 */

const app = new Vue({
    el: '#app',

    data: {

        messages:[]
    },

    created() {
        this.fetchMessages();

        Echo.private('chat')
            .listen('MessageSent', (e) => {
                this.message.push({
                    message: e.message.message,
                    user: e.user
                });
            });
    },




    methods: {
        fetchMessages() {
            axions.get('/messages').then(response => {
                this.messages = response.data;
            });
        },

        addMessage(message) {
            this.message.push(message);

            axios.post('/messages', message).then(response => {
                console.log(response.data);
            });
        }
    }
});