visdiff: Use clone instead of worktree
visdiff: Use clone instead of worktree

The worktree command is not available until git v2.5. :(

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client