Remove redundant to_s

Author: Shuhei Kitagawa

lib/extensions/has_one.rb

@@ -11,7 +11,7 @@ def self.define_accessors(mixin, reflection)
       super
       name = reflection.name
       mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name.to_s}_id
+        def #{name}_id
           association(:#{name}).reader.try(:id)
         end
       CODE