Add field name to TargetMap flatbuffer

We'll use this to know which map we're using in code once we load it on
the robot.

Signed-off-by: Milind Upadhyay <milind.upadhyay@gmail.com>
Change-Id: Id54b82e7b7f07b767a84e266d47468973cbe319e
diff --git a/frc971/vision/target_map.fbs b/frc971/vision/target_map.fbs
index 8adaaaa..50a9d7d 100644
--- a/frc971/vision/target_map.fbs
+++ b/frc971/vision/target_map.fbs
@@ -21,4 +21,7 @@
 // This would be solved for by TargetMapper
 table TargetMap {
   target_poses:[TargetPoseFbs] (id: 0);
+
+  // Unique name of the field
+  field_name:string (id: 1);
 }
\ No newline at end of file