Travis Rebuild on HERMIT changes

[andygill]

Figure out how to force travis to rebuild when the hermit repo changes. HERMIT changes may break the build.

[xich]

I'll set up the hermit travis build to clone hermit-shell and build it...

[andygill]

I've got the hermit-shell building, and running the shell tests (finally!).

[andygill]

For now, I've added a .hermit file, that contains the md5 of the latest HERMIT checkin. Edit this file is a cheap, but not automated, way to force a travis rebuild.

[RyanGlScott]

If you want to avoid having to make a repo change to trigger a build, there are two other ways I know of doing it:

1. From the GitHub repo, go to Settings > Webhooks & Services > Travis CI, then click the "Test service" button in the top-right corner.
2. You can use the travis.rb CLI app to restart the last build with travis restart.