py2cairo: use options DSL

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/py2cairo.rb

@@ -8,18 +8,16 @@ class Py2cairo < Formula
   depends_on 'cairo'
   depends_on :x11
 
+  option :universal
+
   fails_with :llvm do
     build 2336
     cause "The build script will set -march=native which llvm can't accept"
   end
 
-  def options
-    [['--universal', 'Build universal binaries']]
-  end
-
   def install
     # Python extensions default to universal but cairo may not be universal
-    unless ARGV.build_universal?
+    unless build.universal?
       ENV['ARCHFLAGS'] = if MacOS.prefer_64_bit?
         "-arch x86_64"
       else