This PR updates our minimum supported Chrome version from 63 to 66, so that we may use the `AbortController` browser API without polyfilling it.
Our minimum Firefox version supports the `AbortController`, but our current minimum Chrome version (63, released in December 2017) does not. Chrome shipped the `AbortController` in version 66, in April 2018. We have determined that an extremely small number of users are on Chrome 63 < 66, and that this change is therefore acceptable.
The Chrome minimum version has been increased from v58 to v63. We found
that we had very few users on versions below v63, and v62 is
incompatible with our SES lockdown dependency.
This also makes us compatible with Object rest/spread syntax, so we
might not have to transpile that anymore. I'll revisit that separately.
The `externally_connectable` property of the extension manifest is not
recognized by Firefox. It has been moved from the base manifest to the
Chrome manifest, so that we no longer get a warning about this property
on Firefox.
We would like to eventually remove it from the Chrome manifest as well,
but we'll wait until we can batch it with other permission changes so
that it doesn't unnecessarily re-prompt the user (see #9804)
Instead of using `eslint-plugin-json` for linting JSON files,
`prettier` is now used. `prettier` is capable of detecting and
correcting more problems than `eslint-plugin-json` can, such as
indentation.
All JSON files have been run through `prettier`. The changes are all
superficial.
