We're using Circle CI for testing a bunch of the spec, and so far it has the advantage of being faster. Also, it's not named the same as me.
We can also remove the Travis CI specific check in generate-matrix-org-assets because Circle CI doesn't touch this.
Having the jekyll assets here is a mistake, because they need to be versioned
separately to the spec: we keep old versions of the spec, but they sometimes
need to be restyled to match the latest website.