Add "update-vendor.sh" script and vendor our current deps (minus Docker, since that'd make a circle)

Also, updated .travis.yml to use the new "vendor" directory (since this is pretty pointless without that :D)

Signed-off-by: Andrew Page <admwiggin@gmail.com>
Run update-vendor.sh to vendor our deps

Signed-off-by: Andrew Page <admwiggin@gmail.com>