Upgrade libpng

Author: certik

pkgs/png.yaml

@@ -4,8 +4,8 @@ dependencies:
   run: [zlib]
 
 sources:
-- url: http://sourceforge.net/projects/libpng/files/libpng16/older-releases/1.6.6/libpng-1.6.6.tar.gz
-  key: tar.gz:dj4va2fjpzsuvcl3usxe76jiywh6phjz
+- key: tar.gz:43flhdyfdp6gneu6ozwb4z7lu35pvspa
+  url: http://sourceforge.net/projects/libpng/files/libpng16/older-releases/1.6.14/libpng-1.6.14.tar.gz
 
 when_build_dependency:
   - prepend_path: PKG_CONFIG_PATH