Update active_record_callbacks.md

Co-authored-by: NJonathan Hefner <jonathan@hefner.pro>

guides/source/active_record_callbacks.md

@@ -431,7 +431,7 @@ end
 NOTE: The `:on` option specifies when a callback will be fired. If you
 don't supply the `:on` option the callback will fire for every action.
 
-Since using `after_commit` callback only on create, update, or delete is
+Since using the `after_commit` callback only on create, update, or delete is
 common, there are aliases for those operations:
 
 * `after_create_commit`