fix doc: 'brew cask install smcfancontrol' => 'brew install --cask smcfancontrol'

```
$ brew cask install smcfancontrol
Error: Unknown command: cask
$ brew install --cask smcfancontrol
$ brew install --cask smcfancontrol
==> Downloading https://www.eidac.de/smcfancontrol/smcfancontrol_2_6.zip
######################################################################## 100.0%
==> Installing Cask smcfancontrol
...
🍺  smcfancontrol was successfully installed!
```