Wrong version in setup.py

According to gitlab log (and tags) the most recent version of the library should be 2021.3, but the version number listed inside setup is 2021.1 [1]

[1] https://gitlab.lrz.de/tum-cps/commonroad-drivability-checker/-/blob/master/setup.py#L13

Hi Alessio,

thanks for spotting that, we will change this.

Best,
Gerald