init: Add '-c' as an alias to '--current-branch'
init: Add '-c' as an alias to '--current-branch'

This makes it consistent with the short option for current-branch in
repo sync.

Change-Id: I2848e87f45a66ef8d829576d0c0c4c0f7a8636a0
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/241700
Tested-by: Diogo Ferreira <b887df8c61675329470d1091fc61d83d66000760@gmail.com>
Reviewed-by: David Pursehouse <e7b5c6a4a3dbaca972851f8c075e19915752593f@collab.net>
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

mer-tools/git-repo,aosp-mirror/tools_repo,lewixliu/git-repo,codetutil/git-repo,lipro-yocto/git-repo,TheQtCompany/git-repo,GerritCodeReview/git-repo,TheQtCompany/git-repo,lipro-yocto/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,mer-tools/git-repo,lewixliu/git-repo,GerritCodeReview/git-repo,couchbasedeps/git-repo,codetutil/git-repo