Adding tool to patch lib/BUCK with locally built YANG tools.

Change-Id: Ie026a42aa5cfdd3608a78eb0757bb35cc0048683
diff --git a/.gitignore b/.gitignore
index c5329f4..5ad59bd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,6 +20,7 @@
 .watchmanconfig
 
 /bin/
+lib/yang
 
 web/gui/src/main/webapp/tests/node_modules
 web/gui/src/test/_karma/node_modules