Fix some premature reloads with chokidar awaitWriteFinish

[evrys]

Fixes some cases of #34 where miniflare reloads the worker js file as it is being written to (e.g. by webpack), rather than when it has finished emitting. Seems to particularly be a problem on Windows.

[mrbbot]

Hey! 👋 Thanks for the PR! 🙂

Unfortunately, I haven't had time to maintain Miniflare 1, so it's kinda in limbo...

However, I've been working on Miniflare 2 which is hopefully going to be released very soon. You can try out a pre-release with npm i miniflare@next, find the full changelog here, and migration guide here.