Bumping buck version to use yang-tools 2.1 and new onos buck plugin

Change-Id: I6bf165ac0270114d3a7ee66af5e2d8af33f42a16
diff --git a/tools/build/onos-buck b/tools/build/onos-buck
index 1153958..97da071 100755
--- a/tools/build/onos-buck
+++ b/tools/build/onos-buck
@@ -5,8 +5,8 @@
 
 set -e
 
-BUCK_URL="http://onlab.vicci.org/onos/third-party/buck-v2017.05.09.01.zip"
-BUCK_SHA="fd5179b9945194bdea3d6fe141f7746af03bb2bd"
+BUCK_URL="http://onlab.vicci.org/onos/third-party/buck-v2017.05.25.01.zip"
+BUCK_SHA="3803bc4ee74504e8c590dac5943c9abaf6ba6157"
 
 [  "-U" = "$1" ] && shift && FORCE_UPDATE=True