Add --universal to the libsodium Homebrew formula

universal.diff

diff --git a/Library/Formula/libsodium.rb b/Library/Formula/libsodium.rb
index 31b76a2..75c6c0f 100644
--- a/Library/Formula/libsodium.rb
+++ b/Library/Formula/libsodium.rb
@@ -5,7 +5,10 @@ class Libsodium < Formula
   url 'http://download.dnscrypt.org/libsodium/releases/libsodium-0.3.tar.gz'
   sha1 '3d486dc40e7cbd9542d00088d3b73a719d7746fa'
 
+  option :universal
+
   def install
+    ENV.universal_binary if build.universal?
     system "./configure", "--disable-debug", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"
     system "make check"