poky.conf: bump version for 4.2.4 release

(From meta-yocto rev: 62fb88d93c7a706ed191df71dc67f80b47e7c602)

Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta-poky/conf/distro/poky.conf

@@ -1,6 +1,6 @@
 DISTRO = "poky"
 DISTRO_NAME = "Poky (Yocto Project Reference Distro)"
-DISTRO_VERSION = "4.2.3"
+DISTRO_VERSION = "4.2.4"
 DISTRO_CODENAME = "mickledore"
 SDK_VENDOR = "-pokysdk"
 SDK_VERSION = "${@d.getVar('DISTRO_VERSION').replace('snapshot-${METADATA_REVISION}', 'snapshot')}"