Build Notes for DotNet Needs Updated wget (18.04 Ubuntu)

[futjrn]

in build notes for dotnet the wget is deprecated due to the
wget -q https://packages.microsoft.com/config/ubuntu/**16.04**/packages-microsoft-prod.deb

and should be
wget -q https://packages.microsoft.com/config/ubuntu/**18.04**/packages-microsoft-prod.deb