Bump Newtonsoft.Json in /Demos/MVC/GroupDocs.Signature.MVC.Test

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 12.0.1 to 13.0.2.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](JamesNK/Newtonsoft.Json@12.0.1...13.0.2)

---
updated-dependencies:
- dependency-name: Newtonsoft.Json
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Demos/MVC/GroupDocs.Signature.MVC.Test/packages.config

@@ -14,7 +14,7 @@
   <package id="MvcContrib" version="2.0.95.0" targetFramework="net461" />
   <package id="MvcContrib.TestHelper" version="2.0.95.0" targetFramework="net461" />
   <package id="MvcRouteTester" version="1.2.1" targetFramework="net461" />
-  <package id="Newtonsoft.Json" version="12.0.1" targetFramework="net461" />
+  <package id="Newtonsoft.Json" version="13.0.1" targetFramework="net461" />
   <package id="NUnit" version="3.11.0" targetFramework="net461" />
   <package id="NUnit3TestAdapter" version="3.11.2" targetFramework="net461" />
   <package id="RhinoMocks" version="3.6" targetFramework="net461" />