Contribs: update PNG to 1.6.14

(cherry picked from commit 46aa9db68489337e05019d5ac3388b55e45bbe6f)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/png/SHA512SUMS

-7cdf40b51a29f4df6f5be2c6946de80aa74c54169ceef2ed089fad21bf035b5672ad7e8983ca4d72edd4bb84c9d4e0077479a20e526e27685d30da03230bbb91  libpng-1.6.12.tar.xz
+18cd8f59f5920a04f95e6b200affa6a2a9091a79b3e8d01931c95bad1680495f189c87cb912573c23a6681bf764cd981a97b5efc502cf90892b434db422b1892  libpng-1.6.14.tar.xz

contrib/src/png/rules.mak

 # PNG
-PNG_VERSION := 1.6.12
+PNG_VERSION := 1.6.14
 PNG_URL := $(SF)/libpng/libpng16/$(PNG_VERSION)/libpng-$(PNG_VERSION).tar.xz
 
 PKGS += png