Bumped version of gRPC to 1.3.1

Change-Id: I7798476bd443a796e0e6a6e149ab8f66435ba4fa
diff --git a/drivers/p4runtime/BUCK b/drivers/p4runtime/BUCK
index 09c9bf7..0c9f23d 100644
--- a/drivers/p4runtime/BUCK
+++ b/drivers/p4runtime/BUCK
@@ -1,4 +1,4 @@
-GRPC_VER = '1.3.0'
+GRPC_VER = '1.3.1'
 
 COMPILE_DEPS = [
     '//lib:CORE_DEPS',