dev-vcs/hub: Add LICENSE (MIT)

Since the fourth day of its existence (2009-12-08), Hub has been
distributed under the MIT license [1,2].

[1]: https://github.com/defunkt/hub/blob/master/LICENSE
[2]: https://github.com/defunkt/hub/commit/c7e27f43210f5195d9c6fdcb0a8e87246b914abf
Merge pull request #4 from wking/hub-license

dev-vcs/hub: Add LICENSE (MIT)