add derivation possibility to class definition

lib/parser/module_definition.rb

@@ -7,7 +7,7 @@ module Parser
     end
 
     rule(:class_definition) do
-      keyword_class >> module_name >> eol >>
+      keyword_class >> module_name >> (smaller >> module_name).maybe.as(:derived_name) >> eol >>
       ( (keyword_end.absent? >> root_body).repeat()).as(:class_expressions) >> keyword_end >> newline
     end