change GeneratedFeatureMethods to GeneratedAssociationMethods in docs

the module name was changed in 8e814a0a

activerecord/lib/active_record/associations.rb

@@ -285,7 +285,7 @@ def association_instance_set(name, association)
     #   end
     #
     # If your model class is <tt>Project</tt>, the module is
-    # named <tt>Project::GeneratedFeatureMethods</tt>. The GeneratedFeatureMethods module is
+    # named <tt>Project::GeneratedAssociationMethods</tt>. The GeneratedAssociationMethods module is
     # included in the model class immediately after the (anonymous) generated attributes methods
     # module, meaning an association will override the methods for an attribute with the same name.
     #