Package cl depreciated and giving warnings as of Emacs 27

Package `cl` is depreciated and replaced by `cl-lib`, and as of Emacs 27, user gets warning on startup that `Package cl is depreciated`.

Ref:
- https://github.com/hlissner/doom-emacs/issues/3372#issuecomment-643567913
- https://github.com/kiwanami/emacs-epc/issues/35

Looks like the only required change is to update `cl` to `cl-lib` in line 34.

I'll create a pull request, but opening an issue too in case someone knows something I don't.