動かない例
invoke active_record /Users/thr3a/.rvm/gems/ruby-2.2.1/gems/activerecord-4.2.4/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec': Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord). (Gem::LoadError)
いやgem "mysql2"
入れてるからw
ただのバグっぽい
Gemfile.lock
削除してGemfileで旧バージョンを指定してあげる
gem 'mysql2', '~> 0.3.20'
でbundle install
すればおk