Cheffile cleanup and better caching

Librarian is no longer keeping the `:path` as part of the cache key, so caching is much more effective with librarian v1.1.2 for the way you use cookbooks. First run should be significantly faster :)
https://github.com/applicationsonline/librarian/commit/f47d61d9d321a040d4c24eeb0bf1676c8526b21f

And yeah, moved to using the cleaner `:github => 'pivotal-sprout/blah'` format

Nothing else of substance changed!