Fix URL of Bodhi in staging
    
    Otherwise, it errors out like this:
    
    ```
    $ fedpkg-stage build
    Could not execute build: Invalid URL 'bodhi.stg.fedoraproject.org/releases//?exclude_archived=True': No scheme supplied. Perhaps you meant https://bodhi.stg.fedoraproject.org/releases//?exclude_archived=True?
    ```
    
    Signed-off-by: Nils Philippsen <nils@redhat.com>