[Rails5] Add FALSE_VALUES constant to Service#boolean_accessor

In Rails 5.0 the `ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES`
constant has been removed [1] and the remaining `FALSE_VALUES` constant
has been moved to `ActiveModel::Type::Boolean` [2]

[1]: a502703c3d
[2]: 9cc8c6f373

app/models/service.rb

@@ -206,7 +206,11 @@ class Service < ActiveRecord::Base
     args.each do |arg|
       class_eval %{
         def #{arg}?
-          ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES.include?(#{arg})
+          if Gitlab.rails5?
+            !ActiveModel::Type::Boolean::FALSE_VALUES.include?(#{arg})
+          else
+            ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES.include?(#{arg})
+          end
         end
       }
     end