[skip ci] Use GitHub's URL shortener (#686)

git.io is GitHub's own URL shortener, which is guaranteed to only point to GitHub domains. This is safer and (IMO) more professional. Additionally, goo.gl will be deprecated *very* soon.

Author: turbo

README.md

@@ -90,7 +90,7 @@ configuration options [here](docs/operating/options.md). If you are on Windows,
 Install the IronFunctions CLI tool:
 
 ```sh
-curl -LSs https://goo.gl/VZrL8t | sh
+curl -LSs git.io/ironfn | sh
 ```
 
 This will download a shell script and execute it.  If the script asks for a password, that is because it invokes sudo.