Git tag failure isn't handled

Context

When using changeset publish or changeset tag if for some reason git tag fails, no error is reported. Only this message is displayed which can be misleading because it seems to indicate success :

New tag: $TAG

Problem

When using changeset publish the program doesn't exit with an error and moves forward with publishing the packages even though the tags have not been created. While using changesets in a CI where git is not configured correctly for instance, this can lead to an unnecessary waste of time trying to figure out why the tags aren't created properly (happened to my team and I :p)

Proposed Solution

Check the command exit code and throw an error in case of failure I've a created a PR to fix that