Fix bad method signature

Summary: This ended up having a different signature; the discrepancy can cause a warning.

Test Plan: No more warning.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11971

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -186,7 +186,9 @@ abstract class PhabricatorApplicationTransactionEditor
     return $this->unmentionablePHIDMap;
   }
 
-  protected function shouldEnableMentions() {
+  protected function shouldEnableMentions(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
     return true;
   }