Fix arrow function parens arguments

[dodev]

The syntax highlighter showed error when arrow functions had parentheses surrounding their arugemnts:

...
  .then((result) => {
      send(result);
  })
--^ // The last parenthesis of `then` method call was considered excess.

I fixed the regex for args in parenthesis and it seems it works. I'm using it right now.

[davidchambers]

This appears to fix #364. Please open a new pull request against the develop branch, @dodev. Thanks!