Fixes #58 (#61)

Author: Seth

dart.rb

@@ -3,7 +3,7 @@ class Dart < Formula
  homepage "https://www.dartlang.org/"
 
  version "2.1.0"
- if MacOS.prefer_64_bit?
+ if Hardware::CPU.is_64_bit?
  url "https://storage.googleapis.com/dart-archive/channels/stable/release/2.1.0/sdk/dartsdk-macos-x64-release.zip"
  sha256 "5576013b2d5e03f3d8cb85a6cd8820fec2c9a856c1510c0666ff2157065aa76a"
  else
@@ -13,7 +13,7 @@ class Dart < Formula
 
  devel do
  version "2.1.1-dev.0.1"
- if MacOS.prefer_64_bit?
+ if Hardware::CPU.is_64_bit?
  url "https://storage.googleapis.com/dart-archive/channels/dev/release/2.1.1-dev.0.1/sdk/dartsdk-macos-x64-release.zip"
  sha256 "1ea3708c05aa9ead81783a0098c23a964ae081787f7f5d064d66aabefca15bb2"
  else

dart@1.rb

@@ -5,7 +5,7 @@ class DartAT1 < Formula
 
  keg_only :versioned_formula
 
- if MacOS.prefer_64_bit?
+ if Hardware::CPU.is_64_bit?
  url "https://storage.googleapis.com/dart-archive/channels/stable/release/1.24.3/sdk/dartsdk-macos-x64-release.zip"
  sha256 "3419869401184d1ebf44e8947de36ac83ff614097c2c52a80792e89a25c18cd8"
  else

dart@2.rb

@@ -5,7 +5,7 @@ class DartAT2 < Formula
 
  keg_only :versioned_formula
 
- if MacOS.prefer_64_bit?
+ if Hardware::CPU.is_64_bit?
  url "https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip"
  sha256 "7cb9e65cea94ce23b05af4e5224ec416b26c3fb6bf0718778b68f6a73e617cc3"
  else