herokuのpostgresでDatetime field overflow　をなおしたい

前提・実現したいこと

Laravelでgithub認証を実装しています。
その際にローカル環境では問題なく、動くのですが、herokuにデプロイしてからgithubアカウントでログイン認証を行うと、Datetime field overflow が発生し、正常にログイン先のページが表示されません。

datetime fieldはどのような形にすべきで、何故発生するのかを教えていただきたく。

発生している問題・エラーメッセージ

SQLSTATE[22008]: Datetime field overflow: 7 ERROR: date/time field value out of range: "20/06/21 17:15:35" HINT: Perhaps you need a different "datestyle" setting. (SQL: insert into public.user (github_id,created_at,updated_at) values (moriokameda,20/06/21 17:15:35,20/06/21 17:15:35))

該当のソースコード

LoginController.php

php
1<?php
2
3namespace App\Http\Controllers\Auth;
4
5use App\Http\Controllers\Controller;
6use Illuminate\Foundation\Auth\AuthenticatesUsers;
7use Illuminate\Http\Request;
8use Illuminate\Support\Facades\DB;
9use Socialite;
10
11class LoginController extends Controller
12{
13    /*
14    |--------------------------------------------------------------------------
15    | Login Controller
16    |--------------------------------------------------------------------------
17    |
18    | This controller handles authenticating users for the application and
19    | redirecting them to your home screen. The controller uses a trait
20    | to conveniently provide its functionality to your applications.
21    |
22    */
23
24    use AuthenticatesUsers;
25
26    /**
27     * Where to redirect users after login.
28     *
29     * @var string
30     */
31    protected $redirectTo = '/home';
32
33    /**
34     * Create a new controller instance.
35     *
36     * @return void
37     */
38    public function __construct()
39    {
40        $this->middleware('guest')->except('logout');
41    }
42
43    /**
44     * githubの認証ページへリダイレクト
45     */
46    public function redirectToProvider() {
47        return Socialite::driver('github')->scopes(['read:user', 'public_repo'])->redirect();
48    }
49
50    /**
51     * githubからユーザ情報を取得
52     *
53     * @return \Illuminate\Http\Response
54     */
55    public function handleProviderCallback(Request $request) {
56
57        $github_user = Socialite::driver('github')->stateless()->user();
58        $now = date('y/m/d H:i:s');
59        $app_user = DB::select('select * from public.user where github_id = ?', [$github_user->user['login']]);
60
61        if (empty($app_user)) {
62            # code...
63            DB::insert('insert into public.user (github_id,created_at,updated_at) values (?,?,?)', [$github_user->user['login'], $now, $now]);
64        }
65
66        $request->session()->put('github_token', $github_user->token);
67        return redirect('github');
68    }
69}
70

2020_06_18_120744_create-table.php

php
1<?php
2
3use Illuminate\Support\Facades\Schema;
4use Illuminate\Database\Schema\Blueprint;
5use Illuminate\Database\Migrations\Migration;
6
7class CreateTable extends Migration
8{
9    /**
10     * Run the migrations.
11     *
12     * @return void
13     */
14    public function up()
15    {
16        //
17        Schema::create('user', function (Blueprint $table) {
18            $table->increments('id');
19            $table->string('name')->nullable();
20            $table->string('comment')->nullable();
21            $table->string('github_id');
22            $table->timestamps();
23        });
24    }
25
26    /**
27     * Reverse the migrations.
28     *
29     * @return void
30     */
31    public function down()
32    {
33        //
34        Schema::drop('user');
35    }
36}