Move from gunk/urljoiner to urljoiner.
Move from gunk/urljoiner to urljoiner.

[#128626207]

Signed-off-by: Brandon Shroyer <d370be3f39cb88690ed16d1a7b77debc20949e86@pivotal.io>

cloudfoundry-incubator/bbs,cloudfoundry-incubator/bbs