UnitsNet.sln: Add .nuspec files to Build solution folder
UnitsNet.sln: Add .nuspec files to Build solution folder

Easier to edit these when bumping versions.

anjdreas/UnitsNet,anjdreas/UnitsNet,BrandonLWhite/UnitsNet,neutmute/UnitsNet,BoGrevyDynatest/UnitsNet,BrandonLWhite/UnitsNet