Updated gfortran.rb

[toyoxx]

Substituted MacOS.prefer_64_bit? for Hardware::CPU.is_64_bit? to allow new Homebrew installations tap on ros/deps

[Coffee-Boyy]

To use this tap until the PR gets pulled in, do:
brew tap toyoxx/homebrew-deps

[mattkanwisher]

Any reason why its taking a year to merge this in?

[HeroCC]

+1 -- as the MacOS homebrew install docs are updated for melodic, it would be great to have this merged!

EDIT I ran into this error, not sure if this is an upstream issue or something related to this patch, would appreciate your feedback @toyoxx

brew tap toyoxx/homebrew-deps                                                                                                                                                                                                                      1
==> Tapping toyoxx/deps
Cloning into '/usr/local/Homebrew/Library/Taps/toyoxx/homebrew-deps'...
remote: Enumerating objects: 108, done.
remote: Total 108 (delta 0), reused 0 (delta 0), pack-reused 108
Receiving objects: 100% (108/108), 28.61 KiB | 1010.00 KiB/s, done.
Resolving deltas: 100% (49/49), done.
Error: Invalid formula: /usr/local/Homebrew/Library/Taps/toyoxx/homebrew-deps/gfortran.rb
gfortran: private method `include?' called for #<BuildOptions:0x00007f87828a7580>
Error: Cannot tap toyoxx/deps: invalid syntax in tap!