Ruby: fix class name reference of nested model

and model name in underscore format, e.g. "my_response".

Closes #2140

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/RubyClientCodegen.java

@@ -316,7 +316,7 @@ public class RubyClientCodegen extends DefaultCodegen implements CodegenConfig {
         if (type == null) {
             return null;
         }
-        return type;
+        return toModelName(type);
     }
 
     @Override