Update homebrew formula URL, again

Unlike previous commit, use link to main branch.

Author: greghendershott

doc/racket-mode.org

@@ -99,7 +99,7 @@ NOTE: If you get an error message about "contacting a host" or "downloading an a
 
 ** Minimal Racket
 
-If you have installed the minimal Racket distribution (for example by using the [[https://github.com/Homebrew/homebrew-core/blob/ebd95ad1db5c23b5b76a4a6aaaa60b1e0b58655e/Formula/m/minimal-racket.rb][homebrew formula]]) Racket Mode needs some additional Racket packages. A simple way to get all these packages is to install the ~drracket~ Racket package. In a command shell:
+If you have installed the minimal Racket distribution (for example by using the [[https://github.com/Homebrew/homebrew-core/blob/master/Formula/m/minimal-racket.rb][homebrew formula]]) Racket Mode needs some additional Racket packages. A simple way to get all these packages is to install the ~drracket~ Racket package. In a command shell:
 
 #+BEGIN_SRC shell
 raco pkg install --auto drracket