Cleanup stale vendored code

[sudo-bmitch]

Bug Report

Current Behavior

Running vendorme doesn't cleanup previously vendored versions.

Expected Behavior

Code that is not currently configured to be vendored shouldn't be included in the vendor directory of project.

Possible Solution

Running vendor.sh could clean old versions before vendoring new code.

Steps to Reproduce

1. Update the version in the vendor.yaml and see the old version remain in the directory.

Your Environment

Linux