Remove return from example addAction

Signed-off-by: Matthew Peveler <matt@popsql.com>

monaco-editor/website/playground/new-samples/interacting-with-the-editor/adding-an-action-to-an-editor-instance/sample.js

@@ -48,6 +48,5 @@ editor.addAction({
 	// @param editor The editor instance is passed in as a convenience
 	run: function (ed) {
 		alert("i'm running => " + ed.getPosition());
-		return null;
 	}
 });