bump yang-tools version to 2.4.7

Change-Id: I0a257b8b524cd7f6e606d57e6d1a3a5388646ebe
diff --git a/tools/dev/bin/patch-yang-libs b/tools/dev/bin/patch-yang-libs
index 8504acb..52419f1 100755
--- a/tools/dev/bin/patch-yang-libs
+++ b/tools/dev/bin/patch-yang-libs
@@ -3,7 +3,7 @@
 # Patches lib/BUCK file to use locally built YANG tools.
 # -----------------------------------------------------------------------------
 
-BVER=2.4.1
+BVER=2.4.7
 SVER=2.5-SNAPSHOT
 
 YANG_TOOLS_ROOT=${YANG_TOOLS_ROOT:-~/onos-yang-tools}