Support for :credentials on Rails v5.2.x. (#60)

Appraisals

@@ -1,3 +1,8 @@
+appraise 'rails-52' do
+  gem 'actionpack', '~> 5.2.0.beta2'
+  gem 'railties', '~> 5.2.0.beta2'
+end
+
 appraise 'rails-51' do
   gem 'actionpack', '~> 5.1'
   gem 'railties', '~> 5.1'