fix YANG tool version in patch-yang-libs

Change-Id: Id75bf79449f3a927fee54e71a8e19121bfa73604
diff --git a/tools/dev/bin/patch-yang-libs b/tools/dev/bin/patch-yang-libs
index d5a6161..89ebeb6 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=2.2.0-b3
+BVER=2.2.0-b6
 SVER=2.2-SNAPSHOT
 
 YANG_TOOLS_ROOT=${YANG_TOOLS_ROOT:-~/onos-yang-tools}