force proto3, protoc 3.6 compatible

protos/unreal/unreal.proto

@@ -1,3 +1,5 @@
+syntax = 'proto3';
+
 package storyteller.unreal;
 
 // The payloads delivered to unreal engine over the pubsub bus.
@@ -13,27 +15,27 @@ message UnrealEventPayloadV1 {
   }
 
   // Type of the payload.
-  optional PayloadType payload_type = 1;
+  PayloadType payload_type = 1;
 
   // A binary-encoded proto whose type is based on the above value.
-  optional bytes payload = 2;
+  bytes payload = 2;
 }
 
 // Warp within a Cesium geospatial world.
 message CesiumWarpRequest {
   // Required
-  optional double latitude = 1;
+  double latitude = 1;
 
   // Required
-  optional double longitude = 2;
+  double longitude = 2;
 
   // Optional. Fields describing the user that sent the message.
-  optional int64 twitch_user_id = 3;
-  optional string twitch_username = 4;
-  optional bool twitch_user_is_mod = 5;
-  optional bool twitch_user_is_subscribed = 6;
+  int64 twitch_user_id = 3;
+  string twitch_username = 4;
+  bool twitch_user_is_mod = 5;
+  bool twitch_user_is_subscribed = 6;
 
   // Optional. Name of the channel, prefixed with hash. eg. `#vocodes`.
-  optional string twitch_channel = 7;
+  string twitch_channel = 7;
 }