Change pre-commit `rev:` to `master`

Thanks a ton for your work!

Implementing this means one less thing to keep up-to-date in the readme. Current example fails:

[INFO] Initializing environment for https://github.com/bwhmather/ssort.
An unexpected error has occurred: CalledProcessError: command: ('/usr/bin/git', 'checkout', '0.11.5')
return code: 1
expected return code: 0
stdout: (none)
stderr:
    error: pathspec '0.11.5' did not match any file(s) known to git

Whereas new example running, pre-commit automatically informs the user:

[WARNING] The 'rev' field of repo 'https://github.com/bwhmather/ssort' appears to be a mutable reference (moving tag / branch).  
Mutable references are never updated after first install and are not supported.  
See https://pre-commit.com/#using-the-latest-version-for-a-repository for more details.  
Hint: `pre-commit autoupdate` often fixes this.

And pre-commit autoupdate indeed fixes it.

Totals
Change from base Build 2742165713:	0.0%
Covered Lines:	1273
Relevant Lines:	1296

bwhmather / ssort

Change pre-commit `rev:` to `master` #75

Pull Request Test Coverage Report for Build 3080759635

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