webp 0.3.1, add webp-mux flags

Closes Homebrew/homebrew#21080.

Signed-off-by: Misty De Meo <mistydemeo@gmail.com>

Formula/webp.rb

@@ -2,14 +2,17 @@ require 'formula'
 
 class Webp < Formula
   homepage 'http://code.google.com/speed/webp/'
-  url 'http://webp.googlecode.com/files/libwebp-0.3.0.tar.gz'
-  sha1 'a20acf2f180d3eae77e24a63371b01fa412fa2f1'
+  url 'https://webp.googlecode.com/files/libwebp-0.3.1.tar.gz'
+  sha1 '52e3d2b6c0b80319baa33b8ebed89618769d9dd8'
 
   depends_on :libpng
   depends_on 'jpeg' => :recommended
 
   def install
     system "./configure", "--disable-dependency-tracking",
+                          "--enable-libwebpmux",
+                          "--enable-libwebpdemux",
+                          "--enable-libwebpdecoder",
                           "--prefix=#{prefix}"
     system "make install"
   end