Add support for MacOS ARM64 (M1) (#93)

Co-authored-by: Alexander Thomas <athom@google.com>
diff --git a/Formula/dart-beta.rb b/Formula/dart-beta.rb
index 342d95b..711211c 100644
--- a/Formula/dart-beta.rb
+++ b/Formula/dart-beta.rb
@@ -7,9 +7,12 @@
   version "2.14.0-377.7.beta"
 
   conflicts_with "dart", because: "dart ships the same binaries"
-  if OS.mac?
+  if OS.mac? && Hardware::CPU.intel?
     url "https://storage.googleapis.com/dart-archive/channels/beta/release/2.14.0-377.7.beta/sdk/dartsdk-macos-x64-release.zip"
     sha256 "34e0f9af9a45a122b6a3618c3e0f9822e57f09300ca0839b2c4f7138ac476287"
+  elsif OS.mac? && Hardware::CPU.arm?
+    url "https://storage.googleapis.com/dart-archive/channels/beta/release/2.14.0-377.7.beta/sdk/dartsdk-macos-arm64-release.zip"
+    sha256 "dbb2a28b2d3f645171d614d387add13be17b156b09cc20398f2fecf2369accce"
   elsif OS.linux? && Hardware::CPU.intel?
     if Hardware::CPU.is_64_bit?
       url "https://storage.googleapis.com/dart-archive/channels/beta/release/2.14.0-377.7.beta/sdk/dartsdk-linux-x64-release.zip"
diff --git a/Formula/dart.rb b/Formula/dart.rb
index 155145c..fa9a820 100644
--- a/Formula/dart.rb
+++ b/Formula/dart.rb
@@ -7,9 +7,12 @@
 
   head do
     version "2.15.0-65.0.dev"
-    if OS.mac?
+    if OS.mac? && Hardware::CPU.intel?
       url "https://storage.googleapis.com/dart-archive/channels/dev/release/2.15.0-65.0.dev/sdk/dartsdk-macos-x64-release.zip"
       sha256 "9c71429a806dd2ac7968542771764dd5d1b7c71fd03851c6870eb5c3f687fb1b"
+    elsif OS.mac? && Hardware::CPU.arm?
+      url "https://storage.googleapis.com/dart-archive/channels/dev/release/2.15.0-65.0.dev/sdk/dartsdk-macos-arm64-release.zip"
+      sha256 "754521d866bf2e878d2b4a33be96ece27a6381aa4b73a397d0b349bdd87b4eaa"
     elsif OS.linux? && Hardware::CPU.intel?
       if Hardware::CPU.is_64_bit?
         url "https://storage.googleapis.com/dart-archive/channels/dev/release/2.15.0-65.0.dev/sdk/dartsdk-linux-x64-release.zip"