Release process

This is the process for updating the "alpha" branch.

0. Remove the code in the flutter tool that upgrades you from alpha to master.
1. Ensure everything is green on Travis and on the infra bots and on the cocoon dashboard (if you are not a Googler, please ask one to check the dashboard for you).
2. Ensure there are no outstanding bugs in the "Today" milestone.
3. Notify the Flutter Hackers internal Hangout, and the Gitter, that you updating the alpha branch. Wait for a few minutes to make sure people have a chance to let you know of any reason to not release the alpha branch.
4. Ensure your local workspace is configured according to the instructions in Flutter's CONTRIBUTING.md.
5. Run: git fetch upstream
6. Run: git reset upstream/master --hard
7. Run: git push upstream HEAD:alpha
8. Email flutter-dev@googlegroups.com lists notifying them that alpha is updated. Please include a list of changes, if you're aware of them. If you are a Googler, also e-mail the Google-internal flutter-users@google.com list.
9. Done!