Merge pull request #2864 from PikachuEXE/remove-alias-method-chain

* Remove usage of alias_method_chain

Author: mshibuya

lib/rails_admin/adapters/mongoid/extension.rb

@@ -11,7 +11,9 @@ class << self
             def rails_admin(&block)
               RailsAdmin.config(self, &block)
             end
-            alias_method_chain :accepts_nested_attributes_for, :rails_admin
+
+            alias_method :accepts_nested_attributes_for_without_rails_admin, :accepts_nested_attributes_for
+            alias_method :accepts_nested_attributes_for, :accepts_nested_attributes_for_with_rails_admin
           end
         end