CI autoupdate pre-commit versions
Rather than manually updating versions of hooks when new ones come out, we can make a GitHub action to open a PR to do this automatically every Monday.

For this to work, we will need whoever owns the repo to [create an access token](https://github.com/technote-space/create-pr-action#github_token) and add it as secret `ACTION_TRIGGER_TOKEN` to the repo - see screenshot below for an example

![image](https://user-images.githubusercontent.com/33491632/96995872-c9972b00-1526-11eb-9c9f-0e38d754590c.png)
