Fix compatibility with Click 7.0
Fix compatibility with Click 7.0

I'm pretty sure this was tracked somewhere but I can't figure out where.
In any case, click 7.0 seems to have stopped setting
'Command.short_help' by default so you now have to use the new
'Command.get_short_help_str' function instead.

Signed-off-by: Stephen Finucane <06fa905d7f2aaced6dc72e9511c71a2a51e8aead@that.guru>

click-contrib/sphinx-click