use classic way to define method

it is better and faster

lib/geocoder/results/nominatim.rb

@@ -79,7 +79,7 @@ module Geocoder::Result
          polygonpoints display_name class type stadium]
     end
 
-    define_method 'class' do
+    def class
       warn "DEPRECATION WARNING: The 'class' method of Geocoder::Result::Nominatim objects is deprecated and will be removed in Geocoder version 1.2.0. Please use 'place_class' instead."
       @data['class']
     end