Fix warning from protobuf about version of the protobuf file syntax
diff --git a/src/action-item.proto b/src/action-item.proto
index 1bba70f..7bb6f21 100644
--- a/src/action-item.proto
+++ b/src/action-item.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 message ActionItem
 {
   enum ActionType