fix mistake in jerk limit (diff_drive_controller)

Author: schadocalex

diff_drive_controller/src/speed_limiter.cpp

@@ -121,7 +121,7 @@ namespace diff_drive_controller
       const double dv  = v  - v0;
       const double dv0 = v0 - v1;
 
-      const double dt2 = 2. * dt * dt;
+      const double dt2 = dt * dt;
 
       const double da_min = min_jerk * dt2;
       const double da_max = max_jerk * dt2;