Fix serializer class link on guides

The link was pointing out to the master branch instead of the
v-10-stable branch.

Author: feliperenan

docs/general/serializers.md

@@ -452,7 +452,7 @@ serializer classes.
 
 ## More Info
 
-For more information, see [the Serializer class on GitHub](https://github.com/rails-api/active_model_serializers/blob/master/lib/active_model/serializer.rb)
+For more information, see [the Serializer class on GitHub](https://github.com/rails-api/active_model_serializers/blob/0-10-stable/lib/active_model/serializer.rb)
 
 ## Overriding association methods