bump yang-tools version to 2.4.7

Change-Id: I0a257b8b524cd7f6e606d57e6d1a3a5388646ebe
diff --git a/tools/build/onos-buck b/tools/build/onos-buck
index 7dab646..aa5035d 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="2.4.1"
+YANG_VER="2.4.7"
 ONOS_PLUGIN_VER="1.0.3"
 MAVEN_BASE="https://repo1.maven.org/maven2"
 MAVEN_ONOSPROJECT="$MAVEN_BASE/org/onosproject"