Implement long-term Stackage strategy #39
Description
As soon as some out-of-bounds packages got added to Stackage the build failed for hal and it was removed from nightly :(
In 0.1.2 we added pvp-bounds: both-revision so that stack sdist && stack upload don't initially set bounds and we don't have to spend as much time fixing build errors.
That said, we still need to add more LTS/nightly versions of the lib to upcoming Travis builds so we make sure we're aware of any changes as early as possible.