portaudio: use options DSL

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

Formula/portaudio.rb

@@ -7,14 +7,12 @@ class Portaudio < Formula
 
   depends_on 'pkg-config' => :build
 
+  option :universal
+
   fails_with :llvm do
     build 2334
   end
 
-  def options
-    [["--universal", "Build a universal binary."]]
-  end
-
   # Fix PyAudio compilation on Lion
   def patches
     if MacOS.lion?
@@ -23,7 +21,7 @@ class Portaudio < Formula
   end
 
   def install
-    ENV.universal_binary if ARGV.build_universal?
+    ENV.universal_binary if build.universal?
 
     args = [ "--prefix=#{prefix}",
              "--disable-debug",