Chokidar bump

[eklingen]

Summary

Proposed change:

Update optional dependency chokidar from ^2.0.0 to ^3.3.0.

This fixes the warning users get when installing:

warning nunjucks > chokidar > fsevents@1.2.9: One of your dependencies needs to upgrade to fsevents v2: 1) Proper nodejs v10+ support 2) No more fetching binaries from AWS, smaller package size

There are also performance improvements, and fsevents no longer has to be built at install. For more information, see: https://paulmillr.com/posts/chokidar-3-save-32tb-of-traffic/

The API of v3 is the same as v2, except that dotfiles are no longer ignored by default. I don't think this is relevant for nunjucks. The minimum node version is bumped from v6 to v8, but i'm not sure if that matters considering v6 is no longer in maintenance.

Checklist

I've completed the checklist below to ensure I didn't forget anything. This makes reviewing this PR as easy as possible for the maintainers. And it gets this change released as soon as possible.

• Proposed change helps towards purpose of this project.
• Documentation is added / updated to describe proposed change.
• Tests are added / updated to cover proposed change.
• Changelog has an entry for proposed change (if user-facing fix or feature).

[fdintino]

I can't make sense of the appveyor failures, but that's not worth holding up the merge of this. Thank you!

[antonsamper]

@fdintino when is the next planned release?

[fdintino]

Today. Going to spend a short amount of time trying to verify that there aren't actually runtime errors on windows (the appveyor failures) before releasing.