Make the multitargetting on netstandard2.0 working.
Make the multitargetting on netstandard2.0 working.

Need to understand more on why netstandard1.6 does not compile.

mathnet/mathnet-numerics,shaia/mathnet-numerics,shaia/mathnet-numerics,shaia/mathnet-numerics,mathnet/mathnet-numerics,mathnet/mathnet-numerics,shaia/mathnet-numerics,shaia/mathnet-numerics,mathnet/mathnet-numerics,mathnet/mathnet-numerics