Fixed drivetrain code building issue.

Change-Id: I630d61a2122956f62534142c37e8282efc8cdb0c
diff --git a/frc971/control_loops/drivetrain/polydrivetrain.h b/frc971/control_loops/drivetrain/polydrivetrain.h
index 1ba7eee..c482f77 100644
--- a/frc971/control_loops/drivetrain/polydrivetrain.h
+++ b/frc971/control_loops/drivetrain/polydrivetrain.h
@@ -24,7 +24,7 @@
   // Computes the speed of the motor given the hall effect position and the
   // speed of the robot.
   double MotorSpeed(const constants::ShifterHallEffect &hall_effect,
-                    double shifter_position, double velocity);
+                    double shifter_position, double velocity, Gear gear);
 
   // Computes the states of the shifters for the left and right drivetrain sides
   // given a requested state.