yarn 0.15.1 (new formula)

Closes #5821.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/yarn.rb

@@ -0,0 +1,21 @@
+require "language/node"
+
+class Yarn < Formula
+  desc "Javascript package manager"
+  homepage "https://yarnpkg.com/"
+  url "https://registry.npmjs.org/yarn/-/yarn-0.15.1.tgz"
+  sha256 "f99fd587e84987909d5f9e918b8fe524349fdc548e5bc5c380c8f8c0a70c6b87"
+  head "https://github.com/yarnpkg/yarn.git"
+
+  depends_on "node"
+
+  def install
+    system "npm", "install", *Language::Node.std_npm_install_args(libexec)
+    bin.install_symlink Dir["#{libexec}/bin/*"]
+  end
+
+  test do
+    (testpath/"package.json").write('{"name": "test"}')
+    system bin/"yarn", "add", "jquery"
+  end
+end