remove obsolete --cask flag

Author: mheob

README.md

@@ -55,7 +55,7 @@ You can also use [homebrew](https://brew.sh/) as an alternative:
 
 ```bash
 brew tap homebrew/cask-fonts
-brew install --cask font-monaspace
+brew install font-monaspace
 ```
 
 ### Webfonts