Add `yarn run deploy` to CI

[appsforartists]

Would be nice if material-motion-demos.firebaseapp.com site automatically mirrored the GH repo. We may need separate subdomains for develop and stable, and each contributor will likely want their own too (so CI doesn't clobber manually-deployed WIP work).

[appsforartists]

Blocked by #101

[appsforartists]

You can get the author of the most recent commit with

git log --format="%aE" -n 1

We could have a simple lookup table in circle.yml (or somewhere in the repo) that maps author e-mails to subdomains:

"[email protected]": "material-motion-demos-me"

and have the deploy step rewrite .firebaserc to post to the right domain.