Update repository back up handling for wikis
Update repository back up handling for wikis

* Now wikis will follow the same logic as the main repo
  checkout for --prefer-ssh.
* The regular repository and wiki paths both use the same
  function to handle either cloning or updating a local copy
  of the remote repo
* All git updates will now use “git fetch --all --tags”
  to ensure that tags and branches other than master will
  also be backed up

Embed-Engineering/python-github-backup,josegonzalez/python-github-backup,josegonzalez/python-github-backup