message: Fix KalmanFilter comment error
  If there will be measurement before the next predict, `statePost` would be assigned to updated value. So I guess these steps are meant to handle when no measurement and KF only do the predict step.
  ```cpp
  statePre.copyTo(statePost);
  errorCovPre.copyTo(errorCovPost);
  ```
diff: @@ -96,7 +96,7 @@ const Mat& KalmanFilter::predict(const Mat& control)
  // P'(k) = temp1*At + Q
  gemm(temp1, transitionMatrix, 1, processNoiseCov, 1, errorCovPre, GEMM_2_T);
  - // handle the case when there will be measurement before the next predict.
  + // handle the case when there will be no measurement before the next predict.
  statePre.copyTo(statePost);
  errorCovPre.copyTo(errorCovPost);
  