Bump next yang tool version to 2.4 series

Change-Id: I90cd799f2bc263f2b59de961cbfba8fd0abede29
diff --git a/tools/dev/bin/patch-yang-libs b/tools/dev/bin/patch-yang-libs
index edfc2f1..6cd96e7 100755
--- a/tools/dev/bin/patch-yang-libs
+++ b/tools/dev/bin/patch-yang-libs
@@ -4,7 +4,7 @@
 # -----------------------------------------------------------------------------
 
 BVER=2.3
-SVER=2.3-SNAPSHOT
+SVER=2.4-SNAPSHOT
 
 YANG_TOOLS_ROOT=${YANG_TOOLS_ROOT:-~/onos-yang-tools}