Support Shallow Clones

[iamwyza]

The current behavior of octoversion is to fail if the repo checkout is a shallow one. It'd be nice to have the option to support shallow clones with the understanding that the fetch depth needs to be deep enough to find the parent commit with the last tag needed to calculate the version. For very large git repositories or git histories, this can save a substantial amount of time.

[matt-richardson]

Thanks for the suggestion, @iamwyza.

We currently dont have a use case for this approach, but I'd happily review a PR that added that functionality.