The script incorrectly thinks that `gopkg.in/square/go-jose.v2/cipher`
doesn't have a license because it parses `gopkg.in/square` as the
root of the repo, even though `gopkg.in/square/go-jose.v2` is the
root.

Add special handling for gopkg.in packages by grep'ing for the
version that gopkg.in appends to the package name.