avrdude: use spec deps

Formula/avrdude.rb

@@ -5,17 +5,18 @@ class Avrdude < Formula
   url 'http://download.savannah.gnu.org/releases/avrdude/avrdude-5.11.1.tar.gz'
   sha1 '330b3a38d3de6c54d4866819ffb6924ed3728173'
 
-  head 'svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude/'
+  head do
+    url 'svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude/'
 
-  depends_on 'libusb-compat'
-  depends_on 'libftdi0'
-
-  if build.head?
     depends_on :autoconf
     depends_on :automake
     depends_on :libtool
   end
 
+
+  depends_on 'libusb-compat'
+  depends_on 'libftdi0'
+
   def install
     system "./bootstrap" if build.head?
     system "./configure", "--disable-dependency-tracking",