node: Fix style in copy-paste test.

This bug got merged due to a problem with Travis CI.

frontend_tests/node_tests/copy_and_paste.js

@@ -23,4 +23,4 @@ var copy_and_paste = zrequire('copy_and_paste');
     // that this not use markdown syntax, since that feels unnecessary.
     assert.equal(copy_and_paste.paste_handler_converter(input),
                  '[https://zulip.readthedocs.io/en/latest/subsystems/logging.html](https://zulip.readthedocs.io/en/latest/subsystems/logging.html');
-})();
+}());