On an M1 Mac, when running `yarn start`, CPU can spike to 100% CPU, and
sometimes a bunch of `mdworker` instances will get spawned. This seems
to be caused by the file-watching mechanism used in dev to automatically
regenerate the build when something is changed. More specifically, we
are using an older version of `watchify`, which uses an older version of
`chokidar`, which is the package that actually does the watching. v4.0.0
of `watchify` upgrades `chokidar` to v3.x ([1]), which comes with
"massive CPU & RAM consumption improvements" ([2]). After the upgrade,
CPU usage decreases to 20-40%.
[1]: https://github.com/browserify/watchify/blob/master/CHANGELOG.md#400
[2]: https://github.com/paulmillr/chokidar/releases/tag/3.0.0
