libpng: upgrade 1.6.47 -> 1.6.48

Changelog:
============
-  Fixed the floating-point version of the mDCv setter 'png_set_mDCv'.
-  Added #error directives to discourage the inclusion of private
   libpng implementation header files in PNG-supporting applications.
-  Added the CMake build option 'PNG_LIBCONF_HEADER', to be used as an
   alternative to 'DFA_XTRA'.
-  Removed the Travis CI configuration files

(From OE-Core rev: 521fb67a6ae80752c8d3cba1de0e4946e26f6c2f)

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-multimedia/libpng/libpng_1.6.47.bb → meta/recipes-multimedia/libpng/libpng_1.6.48.bb

@@ -11,7 +11,7 @@ DEPENDS = "zlib"
 LIBV = "16"
 
 SRC_URI = "${SOURCEFORGE_MIRROR}/${BPN}/${BPN}${LIBV}/${BP}.tar.xz"
-SRC_URI[sha256sum] = "b213cb381fbb1175327bd708a77aab708a05adde7b471bc267bd15ac99893631"
+SRC_URI[sha256sum] = "46fd06ff37db1db64c0dc288d78a3f5efd23ad9ac41561193f983e20937ece03"
 
 MIRRORS += "${SOURCEFORGE_MIRROR}/project/${BPN}/${BPN}${LIBV}/ ${SOURCEFORGE_MIRROR}/project/${BPN}/${BPN}${LIBV}/older-releases/"