Updated nuget spec.
Updated nuget spec.

* Removed silverlight and netcore 4.5 projects.

anjdreas/UnitsNet,neutmute/UnitsNet,Tirael/UnitsNet,maherkassim/UnitsNet,BrandonLWhite/UnitsNet,anjdreas/UnitsNet,maherkassim/UnitsNet,BrandonLWhite/UnitsNet,BoGrevyDynatest/UnitsNet