[RFC] Add script to manually trigger Travis builds.

Requires [jq](https://stedolan.github.io/jq/) and either a Github token in `GH_TOKEN` or a Travis access token in `TRAVIS_TOKEN`, e.g. `GH_TOKEN=... ./scripts/trigger-build.sh`.
Out of curiosity, what's the issue?  `json.loads()` is part of the standard library, so I would've thought this would be fine.