Copy paste mistake in target maker

[theovincent]

It seems like there is a mistake in the target maker.

https://github.com/isl-org/DirectFuturePrediction/blob/b4757769f167f1bd7fb1ece5fdc6d874409c68a9/DFP/future_target_maker.py#L69

I guess we should substract the mean of the measurements in stead of the value of the measurement in itself.

targets[ns, :len(self.meas_to_predict), :] = ((meas[curr_future_steps][:, self.meas_to_predict] - meas_mean[:, self.meas_to_predict])/meas_std[:, self.meas_to_predict]).transpose() 

@dosovits If what I am saying is true, I would be happy to do a pull request.