Fix undefined package_name error
Fix undefined package_name error

At the moment, if the request to PackageCloud fails, the tool crashes
out, as it tries to print an error containing the `package_name`
variable, which is never defined anywhere. This updates the failure
state to print the URL instead, which is more useful for debugging.

Lostmyname/release_tagger,Lostmyname/release_tagger