Change module path to GitHub repository

[gebi]

make git-backup go-install able, fixes error:

% go install github.com/ChappIO/git-backup/cmd/git-backup@latest go: github.com/ChappIO/git-backup/cmd/git-backup@latest: version constraints conflict:
github.com/ChappIO/git-backup@v1.7.0: parsing go.mod:
module declares its path as: git-backup
but was required as: github.com/ChappIO/git-backup

[gebi]

Hi :)

many thx for your tool, it's a real timesaver!
One thing though is a big cumbersome... not being installable via go install because of the import paths. This PR fixes that and makes git-backup compatible with go bin managers like https://github.com/nao1215/gup

As for the available github releases in this project, i'd rather not use those as they are missing go runtime updates and thus security updates...