Update Newtonsoft.Json to a newer version to avoid the security vulnerability

[AlexBumb]

Is your feature request related to a problem? Please describe. Newtonsoft.Json version 12 (https://www.nuget.org/packages/newtonsoft.json/12.0.3) has a high severity security vulnerability.

Describe the solution you'd like Update Newtonsoft.Json to version 13

Pull request already created -> https://github.com/dmitry-bym/JsonKnownTypes/pull/38