Remove unnecessary fat arrow.

Looks like this was introduced in https://github.com/atom/atom/pull/11369. 
🙈

src/text-editor-component.coffee

@@ -287,7 +287,7 @@ class TextEditorComponent
       # with the menu open.
       @openedAccentedCharacterMenu = false
 
-    @domNode.addEventListener 'keyup', =>
+    @domNode.addEventListener 'keyup', ->
       lastKeydownBeforeKeypress = null
       lastKeydown = null