Update Roslyn #208
Description
Apparently, the only version of Visual Studio 2019 that is still supported is 16.11, so we can update WTG.Analyzers to Roslyn 3.11. Alternatively, mainstream support for Visual Studio 2019 ends in a little under a year; so if we decide that it's not worth supporting Visual Studio 2019 then we can bump Roslyn up to 4.0.1 (or 4.2 in July when support for 17.0 ends).