Fix no-mocha-arrow fixer

[jfmengels]

When a test implementation has parameters, the end result would have missing parens.

it(done => {});
// -->
it(function done {});

This fixes it. I could not keep a consistent spacing for function () {} and function() {}, so I modified the current results, but when fixing, that will probably be taken care of the other rules' fixers anyway.

cc @rhysd if you feel like reviewing

[lo1tuma]

LGTM

[rhysd]

Ah, you're correct. Thank you for the fix.