v0.6.0

• Added githubRelease directive to pull github release assets (vendir.yml spec was updated)

75ebece3fe3b45051ade3045b6e35d351709b42c32ebd4e05c4ea49f11594115  ./vendir-darwin-amd64
c746c2f5a119816970fa5fe22ecffd89cf30a0a2cad68e1882f7fe4700923e71  ./vendir-linux-amd64
d10b763e53c5457205f41a7468ebfbaa4eaef5d4885896c623ae81897776539a  ./vendir-windows-amd64.exe

(Installation instructions: https://k14s.io/#install-from-github-release)