Use npx babel-upgrade --write --install to initiate the upgrade. Then update grunt and rollup.
Decreases minified, gzipped filesize by about 1KB. Decreases build times by a few minutes.
* Switch to es3 preset for babel so that it runs last. Plugins run before presets and presets run in reverse order. Also, we ran into a weird bug in babel that causes `default` not to be quoted in some cases (https://github.com/babel/babel/issues/4799) which we've worked around here.
* Restore the es-shims for tests and the ie8 fallback script.
* Do a null-check around `Player.players`.
* use more round fractions (like 0.5 and 1) to avoid rounding issues.
