Use explicit flatbuffer IDs in y2017 and newer.

Non-explicit ids are risky.  We've seen backwards incompatible
changes...

Change-Id: Id6ceebe031ac80430191f367635d0e951c3d2cbc
diff --git a/y2017/vision/vision.fbs b/y2017/vision/vision.fbs
index f1bc013..7516af1 100644
--- a/y2017/vision/vision.fbs
+++ b/y2017/vision/vision.fbs
@@ -2,15 +2,15 @@
 
 // Published on ".y2017.vision.vision_status"
 table VisionStatus {
-  image_valid:bool;
+  image_valid:bool (id: 0);
 
   // Distance to the target in meters.
-  distance:double;
+  distance:double (id: 1);
   // The angle in radians of the bottom of the target.
-  angle:double;
+  angle:double (id: 2);
 
   // Capture time of the angle using the clock behind monotonic_clock::now().
-  target_time:long;
+  target_time:int64 (id: 3);
 }
 
 root_type VisionStatus;