`skhd` stopped working on MacOS after homebrew upgrade

After running `homebrew upgrade` `skhd` no longer seems to work:

```
$ brew services start skhd
Error: Formula `skhd` has not implemented #plist, #service or installed a locatable service file
$ skhd --version
skhd-v0.3.9
```

Running just `skhd` does work, but kind of breaks my workflow, why does it no longer work with homebrew services?

The issue names no repository file or test. Start by reproducing `brew services start skhd` and compare it with running `skhd` directly; done means the service starts through Homebrew without requiring a foreground process.

Written by the indexing model from the issue text.