Remain unnecessary directory when delete

[zchee]

Hi @FiloSottile, Thanks great vendoring tools :)

BTW, I found a bug(?)
When gvt fetch github.com/zchee/foo, fetch the zchee/foo to $PKG_ROOT/vendor directory. It's ok.
but, If I used gvt delete github.com/zchee/foo, delete $PKG_ROOT/github.com/zchee/foo/* files, but $PKG_ROOT/github.com/zchee/foo directory still remains.
This empty directory will be ignored git flow, but shouldn't vender/github.com/zchee/foo also be deleted?

I think gb also have this problem.(tested) so caused by any internal logic.
I considered that, but post to gvt because I'm using every day.