Add rails 5 to travis matrix

Gemfile

@@ -1,6 +1,13 @@
 source 'https://rubygems.org'
 gemspec
 
+case ENV['RAILS']
+when '5'
+  gem 'actionpack', '5.0.0.rc1'
+when '4'
+  gem 'actionpack', '~> 4.2'
+end
+
 group :development do
   gem 'sdoc', '~> 0.4.1'
   gem 'pry', '~> 0.10.1'