[BUG] Install with --force Flag Overwrites pre-commit.old #162

Running yarn install --force after installing pre-commit causes the pre-commit.old backup to get overwritten by the pre-commit file from this repo

Steps to Reproduce

1. In a new repo, create a pre-commit file with some dummy content

   #!/bin/bash
   echo "Hello World" && exit 0

2. Install pre-commit yarn add pre-commit
3. Notice the pre-commit file is backed up to pre-commit.old
4. Run install with the force flag yarn install --force

Actual Result

• The pre-commit.old backup contents are overwritten with the pre-commit content from this repo

Expected Result

One or both of these options would work:

• additional backup files would be created if pre-commit.old already exists (e.g. pre-commit.old-2)
• a backup file is not created if the contents of pre-commit matches the pre-commit content from this repo