package/libpng: bump version to 1.6.48

Release notes:
https://raw.githubusercontent.com/pnggroup/libpng/v1.6.47/ANNOUNCE
https://raw.githubusercontent.com/pnggroup/libpng/v1.6.48/ANNOUNCE

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/libpng/libpng.hash

@@ -1,5 +1,5 @@
-# From https://sourceforge.net/projects/libpng/files/libpng16/1.6.46/
-sha1  11423f5ea270e7bb42dd2d519696adcd016d5df3  libpng-1.6.46.tar.xz
+# From https://sourceforge.net/projects/libpng/files/libpng16/1.6.48/
+sha1  132bfa1a68e3d8f741d0b3fe03809e181fe57b7d  libpng-1.6.48.tar.xz
 # Locally computed:
-sha256  f3aa8b7003998ab92a4e9906c18d19853e999f9d3bca9bd1668f54fa81707cb1  libpng-1.6.46.tar.xz
+sha256  46fd06ff37db1db64c0dc288d78a3f5efd23ad9ac41561193f983e20937ece03  libpng-1.6.48.tar.xz
 sha256  16d9daaafbf63a31a5bdc91d4600972548fef5aaa1244202393288dbd079c49a  LICENSE

package/libpng/libpng.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-LIBPNG_VERSION = 1.6.46
+LIBPNG_VERSION = 1.6.48
 LIBPNG_SERIES = 16
 LIBPNG_SOURCE = libpng-$(LIBPNG_VERSION).tar.xz
 LIBPNG_SITE = http://downloads.sourceforge.net/project/libpng/libpng$(LIBPNG_SERIES)/$(LIBPNG_VERSION)