Auto merge of #6280 - zachreizner:master, r=dwijnand

Auto merge of #6280 - zachreizner:master, r=dwijnand

use allow-dirty option in `cargo package` to skip vcs checks

If `cargo package` is run for a crate that is not version controlled in
a way that cargo expects, git2 will overreach upwards and grab a
irrelevant .git repo. This change uses `--allow-dirty` to imply to `cargo package` that it should not be checking for version control information, fixing this issue.