Update iojs to v2.4.0 and use CC flag instead of symlink

packages/iojs.rb

 require 'package'
 
 class Iojs < Package
-  version '2.3.4'
-  source_url 'https://iojs.org/dist/v2.3.4/iojs-v2.3.4.tar.gz'
-  source_sha1 '97639c34ebb951a4655ce8b903fa38a3f0135396'
+  version '2.4.0'
+  source_url 'https://iojs.org/dist/v2.4.0/iojs-v2.4.0.tar.gz'
+  source_sha1 'ec273ab80421126c304a6910d8780cae4cbc1276'
 
   depends_on 'buildessential'
   depends_on 'python27'
 
   def self.build
-    # These are needed for iojs to install
-    system "sudo ln -sf /usr/local/bin/gcc /usr/local/bin/cc"
-
-    system "./configure"
+    system "CC='gcc' ./configure"
     system "make"
   end