Search only for .yang files under src/main/yang

Change-Id: I50bfbabf3d55199d9acccfbe7855a2e3da368eda
diff --git a/bucklets/yang.bucklet b/bucklets/yang.bucklet
index 64ff60b..31ce169 100644
--- a/bucklets/yang.bucklet
+++ b/bucklets/yang.bucklet
@@ -38,7 +38,7 @@
 
     yang_library(
       name = yang,
-      srcs = glob(['**/*.yang'], excludes=['**/target/**']),
+      srcs = glob(['src/main/yang/**/*.yang'], excludes=['**/target/**']),
       model_id = model_id
     )