Support both mysql and pg

Gemfile

@@ -9,7 +9,7 @@ end
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 5.1.0'
 # Use mysql as the database for Active Record
-#gem 'mysql2', '>= 0.3.18', '< 0.5'
+gem 'mysql2', '>= 0.3.18', '< 0.5'
 gem 'pg'
 # Use Puma as the app server
 gem 'puma', '~> 3.0'

Gemfile.lock

@@ -233,6 +233,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   jquery-rails
   listen (~> 3.0.5)
+  mysql2 (>= 0.3.18, < 0.5)
   pg
   prawn
   prawn-table