Path separator in MODELICAPATH on Windows issue

https://github.com/lbl-srg/BuildingsPy/blob/1d16ce6650d46202cd62ca8829e4a2be62f00d7b/buildingspy/development/regressiontest.py#L55C1-L58C37

I think this line causes problem when trying to edit the MODELICAPATH on Windows, where the separator is ";" rather than ":". 

I think the line should instead be:

`env['MODELICAPATH'] = os.pathsep.join([worDir, os.environ['MODELICAPATH']])`