Issue #277: 'gearbox install-iis' doesn't work (conservancy/kallithea)

[domruf]

New issue 277: 'gearbox install-iis' doesn't work
https://bitbucket.org/conservancy/kallithea/issues/277/gearbox-install-iis-doesnt-work

domruf:

found by pylint
`Instance of 'Command' has no 'ensure_file' member`

when calling
`gearbox install-iis -c development.ini`
you'll get
`AttributeError: 'Command' object has no attribute 'ensure_file'`