fat_free_crmのインストール

下記サイトを参照にオープンソースをインストールしようとしております。今回、その経過途中のエラーについて解消をしたく質問させて頂きました。

1.ダウンロード（問題なし）

git clone [e-mail]:fatfreecrm/fat_free_crm.git fat_free_crm
cd fat_free_crm


2設定ファイルの作成 config/settings（問題なし）
ここに言語を入力
:locale: "ja"


3データベースの選択（問題なし）（MySQLにて設定を行う）
```ここに言語を入力

Uncomment the database that you have configured in config/database.yml

----------------------------------------------------------------------

gem 'mysql2'

gem 'sqlite3'

gem 'pg'

4budleインストール（問題なし）
```ここに言語を入力
Using rake 12.3.0
Using concurrent-ruby 1.0.5
Using i18n 0.9.3
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 5.1.4
Using builder 3.2.3
Using erubi 1.7.0
Using mini_portile2 2.3.0
Using nokogiri 1.8.2
Using rails-dom-testing 2.0.3
Using crass 1.0.3
Using loofah 2.1.1
Using rails-html-sanitizer 1.0.3
Using actionview 5.1.4
Using rack 2.0.4
Using rack-test 0.8.2
Using actionpack 5.1.4
Using nio4r 2.2.0
Using websocket-extensions 0.1.3
Using websocket-driver 0.6.5
Using actioncable 5.1.4
Using globalid 0.4.1
Using activejob 5.1.4
Using mini_mime 1.0.0
Using mail 2.7.0
Using actionmailer 5.1.4
Using activemodel 5.1.4
Using activemodel-serializers-xml 1.0.2
Using arel 8.0.0
Using activerecord 5.1.4
Using acts-as-taggable-on 5.0.0
Using acts_as_commentable 4.0.2
Using sqlite3 1.3.13
Using acts_as_fu 0.0.9
Using acts_as_list 0.9.10
Using public_suffix 3.0.1
Using addressable 2.5.2
Using net-ssh 4.2.0
Using net-scp 1.2.1
Using sshkit 1.16.0
Using airbrussh 1.3.0
Using io-like 0.3.0
Using archive-zip 0.11.0
Using ast 2.4.0
Using request_store 1.4.0
Using ffi 1.9.18
Using ffi-compiler 1.0.1
Using scrypt 3.0.5
Using authlogic 3.6.1
Using msgpack 1.2.2
Using bootsnap 1.1.8
Using brakeman 4.1.1
Using bundler 1.16.1
Using byebug 10.0.0
Using cancancan 2.1.3
Using capistrano 3.10.1
Using capistrano-bundler 1.3.0
Using capistrano-rails 1.3.1
Using capistrano-rvm 0.1.2
Using xpath 3.0.0
Using capybara 2.17.0
Using childprocess 0.8.0
Using chromedriver-helper 1.2.0
Using chronic 0.10.2
Using climate_control 0.2.0
Using cocaine 0.5.8
Using coderay 1.1.2
Using coffee-script-source 1.12.2
Using execjs 2.7.0
Using coffee-script 2.4.1
Using method_source 0.9.0
Using thor 0.20.0
Using railties 5.1.4
Using coffee-rails 4.2.2
Using i18n_data 0.8.0
Using money 6.10.1
Using sixarm_ruby_unaccent 1.2.0
Using unicode_utils 1.4.0
Using countries 2.1.3
Using sort_alphabetical 1.1.0
Using country_select 3.1.1
Using css_parser 1.6.0
Using database_cleaner 1.6.2
Using diff-lcs 1.3
Using dynamic_form 1.1.4
Using email_reply_parser_ffcrm 0.5.0
Using factory_bot 4.8.2
Using factory_bot_rails 4.8.2
Using ffaker 2.8.1
Using font-awesome-rails 4.7.0.3
Using formatador 0.2.5
Using rb-fsevent 0.10.2
Using rb-inotify 0.9.10
Using ruby_dep 1.5.0
Using listen 3.1.5
Using lumberjack 1.0.12
Using nenv 0.3.0
Using shellany 0.0.1
Using notiffany 0.1.1
Using pry 0.11.3
Using guard 2.14.2
Using guard-compat 1.2.1
Using guard-rails 0.8.1
Using rspec-support 3.7.1
Using rspec-core 3.7.1
Using rspec-expectations 3.7.0
Using rspec-mocks 3.7.0
Using rspec 3.7.0
Using guard-rspec 4.7.3
Using temple 0.8.0
Using tilt 2.0.8
Using haml 5.0.4
Using headless 2.3.1
Using htmlentities 4.3.4
Using jquery-migrate-rails 1.2.1
Using jquery-rails 4.3.1
Using jquery-ui-rails 6.0.1
Using libv8 3.16.14.19 (x86_64-darwin-17)
Using mime-types-data 3.2016.0521
Using mime-types 3.1
Using mimemagic 0.3.2
Using paper_trail 6.0.2
Using paperclip 5.2.1
Using parallel 1.12.1
Using parser 2.4.0.2
Using pg 0.21.0
Using polyamorous 1.3.3
Using powerpack 0.1.1
Using premailer 1.11.1
Using pry-rails 0.3.6
Using puma 3.11.2
Using sprockets 3.7.1
Using sprockets-rails 3.2.1
Using rails 5.1.4
Using rails-controller-testing 1.0.2
Using rails-i18n 5.0.4
Using rails-observers 0.1.5
Using rails3-jquery-autocomplete 1.0.15
Using rails_serve_static_assets 0.0.5
Using rails_stdout_logging 0.0.5
Using rails_12factor 0.0.3
Using rails_autolink 1.1.6
Using rainbow 3.0.0
Using ransack 1.8.7
Using ransack_chronic 1.1.0
Using ransack_ui 1.3.4
Using rb-fchange 0.0.6
Using ref 2.0.0
Using responders 2.4.0
Using responds_to_parent 1.1.0
Using rspec-activemodel-mocks 1.0.3
Using rspec-rails 3.7.2
Using ruby-progressbar 1.9.0
Using unicode-display_width 1.3.0
Using rubocop 0.52.1
Using rubyzip 1.2.1
Using sass-listen 4.0.0
Using sass 3.5.5
Using sass-rails 5.0.7
Using select2-rails 4.0.3
Using selenium-webdriver 3.9.0
Using simple_form 3.5.0
Using therubyracer 0.12.3
Using timecop 0.9.1
Using uglifier 4.1.5
Using will_paginate 3.1.6
Using zeus 0.15.14
Bundle complete! 73 Gemfile dependencies, 169 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.

5マイグレーション（問題発生中）rake db:create↓
``ここに言語を入力
Specified 'mysql2' for database adapter, but the gem is not loaded. Addgem 'mysql2'to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
Couldn't create database for {"adapter"=>"mysql2", "encoding"=>"utf8", "database"=>"fat_free_crm_development", "pool"=>5, "username"=>"root", "password"=>nil, "socket"=>"/var/run/mysqld/mysqld.sock"}
rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Addgem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).

Caused by:
Gem::LoadError: mysql2 is not part of the bundle. Add it to your Gemfile.

Tasks: TOP => db:create
(See full trace by running task with --trace)

上記に記載がある内容はなんとなくわかるのですが、どう解決していいのかが理解できません。サポート頂ければ幸いです。
よろしくお願い致します。