Update Mednafen version and fix Homebrew installer URL

1. Upgrade Mednafen from 0.9.36.3 to 0.9.36.4

1. Fix Homebrew installer URL.  Note that if you run the script as-is you get the following message:

>Whoops, the Homebrew installer has moved! Please instead run:
>
>ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
>
>Also, please ask wherever you got this link from to update it to the above.
Thanks!