Update all JSON.NET use to 11.0 (to support .NET standard 2.0)

[michaelcfanning]

Oops. We said we updated to 11.0 previously but we neglected to update the core SARIF dll.

@eddynaka, take a look. Please merge if you agree with the change.

[eddynaka]

@michaelcfanning , we have to take a look at our .netstandard2.1 reference.
Why:

1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1662,5): warning NU1702: ProjectReference 'C:\Microsoft\sarif-pattern-matcher\Src\sarif-sdk\src\Sarif.Driver\Sarif.Driver.csproj' was resolved using '.NETFramework,Version=v4.7.2' instead of the project target framework '.NETStandard,Version=v2.0'. This project may not be fully compatible with your project.
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1662,5): warning NU1702: ProjectReference 'C:\Microsoft\sarif-pattern-matcher\Src\sarif-sdk\src\Sarif\Sarif.csproj' was resolved using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETStandard,Version=v2.0'. This project may not be fully compatible with your project.

This came from the new spam project...
i think our library should target .netstandard2.0 and our tool can keep using netcoreapp3.1.