added copyright exception for census.proto
diff --git a/tools/distrib/check_copyright.py b/tools/distrib/check_copyright.py
index 611a9f4..9397afc 100755
--- a/tools/distrib/check_copyright.py
+++ b/tools/distrib/check_copyright.py
@@ -111,6 +111,8 @@
 
   # An older file originally from outside gRPC.
   'src/php/tests/bootstrap.php',
+  # census.proto copied from github
+  'tools/grpcz/census.proto',
 ))