Bcryptでcannot load such file --bcryptとでる。

前提・実現したいこと

Rails Tutorialの6章でBcryptをbundle installしたのですが、
Guardで自動化したテストがパスしなくなってしまいました。
このエラーをなくすにはどうしたらよろしいでしょうか？

発生している問題・エラーメッセージ

You don't have bcrypt installed in your application. Please add it to your Gemfile and run bundle install
ERROR["test_email_addresses_should_be_saved_as_lower-case", Minitest::Result

LoadError: cannot load such file -- bcrypt
    app/models/user.rb:8:in `<class:User>'
    app/models/user.rb:1:in `<top

該当のソースコード

class User < ApplicationRecord
  before_save { email.downcase! }
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(.[a-z\d\-]+)*.[a-z]+\z/i
  validates :name, presence: true, length: { maximum: 50 }
  validates :email, presence: true, length: { maximum: 255 },
  format: { with: VALID_EMAIL_REGEX }, uniqueness: { case_sensitive: false }

  has_secure_password
end

test "email addresses should be saved as lower-case" do
    mixed_case_email = "Foo@ExAMPle.CoM"
    @user.email = mixed_case_email
    @user.save
    assert_equal mixed_case_email.downcase, @user.reload.email
  end

source 'https://rubygems.org'

gem 'rails',        '5.1.4'
gem 'bcrypt',       '3.1.11'
gem 'bootstrap-sass', '3.3.7'
gem 'puma',         '3.9.1'
gem 'sass-rails',   '5.0.6'
gem 'uglifier',     '3.2.0'
gem 'coffee-rails', '4.2.2'
gem 'jquery-rails', '4.3.1'
gem 'turbolinks',   '5.0.1'
gem 'jbuilder',     '2.7.0'

group :development, :test do
  gem 'sqlite3', '1.3.13'
  gem 'byebug',  '9.0.6', platform: :mri
end

group :development do
  gem 'web-console',           '3.5.1'
  gem 'listen',                '3.1.5'
  gem 'spring',                '2.0.2'
  gem 'spring-watcher-listen', '2.0.1'
end

group :test do
  gem 'rails-controller-testing', '1.0.2'
  gem 'minitest-reporters',       '1.1.14'
  gem 'guard',                    '2.13.0'
  gem 'guard-minitest',           '2.4.4'
end

group :production do
  gem 'pg', '0.20.0'
end

# Windows環境ではtzinfo-dataというgemを含める必要があります
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]