Automatically deploy babel-bot from master

- Create IAM credentials with bare minimum amount of access
- Add credentials to Travis as `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` environment variables (ideally in the UI so there's no risk of leakage, but encrypted in `travis.yml` is OK too)
- Run `./scripts/deploy.js` after building, on commits to `master` (NOT for PRs)

You might need to adjust `deploy.js` a bit, I made some assumptions when writing it (region is `us-west-1`, function name is `BabelBot`) that might not actually be true.