buildtools: add grpc as a dependency

This will be used by CTP code.

Change-Id: Iaf2be4cae19e5a35072ae0af8d42996018fb2406
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 6682fec..7b11412 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -41,6 +41,7 @@
         files_to_check='.*',
         files_to_skip=[
             'Android[.]bp',
+            "buildtools/grpc/BUILD.gn",
             '.*[.]json$',
             '.*[.]sql$',
             '.*[.]out$',