bump yang tools version to 2.4.1

Change-Id: I146a3196673ddb02eeddb0bd09489419f0196135
diff --git a/tools/build/onos-buck b/tools/build/onos-buck
index 9f5a704..70c4414 100755
--- a/tools/build/onos-buck
+++ b/tools/build/onos-buck
@@ -9,7 +9,7 @@
 BUCK_SHA="45d8bd28f441991257babf89f7a317edb3a2b536"
 
 # onos-yang-tools buck plugin version
-YANG_VER="2.4"
+YANG_VER="2.4.1"
 
 [  "-U" = "$1" ] && shift && FORCE_UPDATE=True