Update libpng from 1.6.28 to 1.6.32

This is a security release addressing a memory leak vulnerability.

Tested as working on XE500C13-K01US. All users of this library should update
their installation.

packages/libpng.rb

@@ -3,21 +3,13 @@ require 'package'
 class Libpng < Package
   description 'libpng is the official PNG reference library.'
   homepage 'http://libpng.org/pub/png/libpng.html'
-  version '1.6.28'
-  source_url 'http://prdownloads.sourceforge.net/libpng/libpng-1.6.28.tar.gz'
-  source_sha256 'b6cec903e74e9fdd7b5bbcde0ab2415dd12f2f9e84d9e4d9ddd2ba26a41623b2'
+  version '1.6.32'
+  source_url 'http://prdownloads.sourceforge.net/libpng/libpng-1.6.32.tar.gz'
+  source_sha256 '1a8ae5c8eafad895cc3fce78fbcb6fdef663b8eb8375f04616e6496360093abb'
 
   binary_url ({
-    aarch64: 'https://dl.bintray.com/chromebrew/chromebrew/libpng-1.6.28-chromeos-armv7l.tar.xz',
-     armv7l: 'https://dl.bintray.com/chromebrew/chromebrew/libpng-1.6.28-chromeos-armv7l.tar.xz',
-       i686: 'https://dl.bintray.com/chromebrew/chromebrew/libpng-1.6.28-chromeos-i686.tar.xz',
-     x86_64: 'https://dl.bintray.com/chromebrew/chromebrew/libpng-1.6.28-chromeos-x86_64.tar.xz',
   })
   binary_sha256 ({
-    aarch64: '52bb5b4d50d0373795d42856bf8fe4d53f6a8353e0254739a242138b600562ec',
-     armv7l: '52bb5b4d50d0373795d42856bf8fe4d53f6a8353e0254739a242138b600562ec',
-       i686: '042b9ed617899e66889e216a7194868bfb286fef7864317c353258a322dcd5f6',
-     x86_64: '11ada0286cff8d7ea6fb4ec22b9149beb87cf5739e32e787691c384ffebd634a',
   })
 
   def self.build