Use
[`command`](https://www.gnu.org/software/bash/manual/bash.html#index-command)
instead of `which` to check if `wild` is installed.

Using `which` will result in an error being printed to stdout: 

```bash
./script/install-wild
which: invalid option -- 's'
/usr/local/bin/wild
Warning: existing wild 0.6.0 found at /usr/local/bin/wild. Skipping installation.
```

Release Notes:

- N/A