12$: Improve diagnostic: f = () {}

[strager]

    client.on('open', () {
      ws.send('something');
    });

Expected: "missing '=>'"

[strager]

Similar:

    client.on('error', error {
      reportError(error);
    });

Expected: "missing '=>' or ','"

[strager]

The looks_like_arrow_function_body variable in parse-expression.cpp looks like a good place to start poking around.

[HicaroD]

I claim this for-hire task. I expect payment after I complete this task. I will email the quick-lint-js team if I am assigned this task.