Fix config reload after vim edit

[chabou]

When vim edit a file, it write a temp file and move it.
In this case, our watcher didn't work anymore.

This PR rewatch file when file is renamed/mv

[albinekb]

We might need to add retry here? 🤔

[chabou]

What would be our retry strategy? Only one time? Retry until it works?
If we think that 500ms is not enough, we need to put some try/catch too.

But I really think that it would work 99.99%. If not, maybe we'll add some retries later?

Mmmmh I should try this with config file remove...

Do not merge it please, I think it needs some more tests on some edge cases

[chabou]

I made a lot of test and it works really great.
I added a try/catch but it should be unused. If a config file is missing, a new one is written: https://github.com/zeit/hyper/blob/24b83615d4f37cfead075c5a80383dac9c3311ee/app/config/import.js#L41

If writing failed, an exception will be shown.
Thus, we can silently (but with log) discard an hypothetical watch exception.
User would have to restart its application to have a config watcher, but this is ok for me because it should not happen.