Fix attribute translator setter

This was simply not working before.

Author: Jell

lib/grape/router/attribute_translator.rb

@@ -38,15 +38,15 @@ def to_h
       end
 
       def method_missing(method_name, *args)
-        if setter?(method_name[-1])
-          attributes[method_name[0..]] = *args
+        if setter?(method_name)
+          attributes[method_name.chomp("=")] = *args
         else
           attributes[method_name]
         end
       end
 
       def respond_to_missing?(method_name, _include_private = false)
-        if setter?(method_name[-1])
+        if setter?(method_name)
           true
         else
           @attributes.key?(method_name)
@@ -56,7 +56,7 @@ def respond_to_missing?(method_name, _include_private = false)
       private
 
       def setter?(method_name)
-        method_name[-1] == '='
+        method_name.end_with?("=")
       end
     end
   end