Release primer-css@9.1.0

[shawnbot]

This is our release branch for v9.1.0 of primer-css, and minor version bumps of all the other submodules.

Changes

• Upgrade to stylelint@7.13.0 (see changes in 7.12.0 for more info) and stylelint-config-primer@2.0.0 in Update stylelint-disable rules; add lint npm scripts #249
• Workflow and CI improvements in Trigger canary release on successful PR build #246 (and this release branch)
• Add PR status messages for published npm versions in Send commit status back after publishing canary release #250

TODO

• Make sure that the RC auto-publishing works the first time around.
• Make sure that the next RC version is published when we push commits.
• Update the change log.
• Because this branch contains additional changes to the CI script, we'll need to merge master back into dev after merging this.

[shawnbot]

Hmm, it's weird that there's a commit status hanging around from (merge commit) 71aa389:

[shawnbot]

I was struggling to get the detection of the release branch to work. (Turns out, when you're testing regular expressions in bash you shouldn't quote the regex!) 🤞 This next commit will trigger a release candidate, and not a PR release.

[shawnbot]

Well, the push build failed because I wasn't setting the branch variable correctly, and the last couple of PR builds dumped core during lerna bootstrap. We'll see...

[shawnbot]

Oh hey, it worked!

[shawnbot]

If anyone's interested, you can see the output from script/cibuild in both the PR build (which doesn't do anything) and the push build (which publishes). I'm on the fence about this distinction, and wonder whether we even really need the separate PR builds on Travis.

[broccolini]