Can't `dvc install` if there is another hook in place

[Casyfill]

Error: failed to install dvc hooks - git hook '.git/hooks/pre-commit' already exists.

[efiop]

Discussed this on ods: we could probably just append a command to what is already in the hook.

@efiop , we would also need to check if they have already added the hook to prevent having the same command twice (i.e. dvc checkout; dvc checkout)

Thanks for reporting the issue, @Casyfill 😃 !

[efiop]

@Casyfill The fix is released as a part of 0.40.1. Please feel free to upgrade and give it a try. Thanks for the feedback! 🙂