Test against Rails 5.2 as latest stable version

.travis.yml

@@ -22,6 +22,7 @@ gemfile:
   - Gemfile.rails4.1
   - Gemfile.rails4.2
   - Gemfile.rails5.0
+  - Gemfile.rails5.1
   - Gemfile.rails-edge
 matrix:
   exclude:

Gemfile

@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-rails_version = '~> 5.1.1'
+rails_version = '~> 5.2.0'
 
 gem 'activerecord', rails_version
 gem 'actionpack',   rails_version
@@ -16,7 +16,7 @@ gem 'dm-migrations'
 gem 'dm-sqlite-adapter'
 gem 'mongoid'
 
-gem 'mysql2', '~> 0.4.6', :group => :mysql
+gem 'mysql2', '~> 0.5.2', :group => :mysql
 gem 'pg', '~> 0.18.4', :group => :pg
 
 group :development do

Gemfile.rails5.1

@@ -0,0 +1,19 @@
+source 'https://rubygems.org'
+
+rails_version = '~> 5.1.1'
+
+gem 'activerecord', rails_version
+gem 'actionpack',   rails_version
+
+gem 'rspec', '~> 2.6.0'
+gem 'mocha', '~> 0.9.8'
+
+gem 'sqlite3', '~> 1.3.6'
+
+gem 'mysql2', '~> 0.5.2', :group => :mysql
+gem 'pg', '~> 0.18.4', :group => :pg
+
+group :development do
+  gem 'ruby-debug', :platforms => :mri_18
+  gem 'debugger', :platforms => :mri_19
+end