Bump Newtonsoft.Json from 6.0.8 to 13.0.1 in /Sources/Agent

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 6.0.8 to 13.0.1.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](JamesNK/Newtonsoft.Json@6.0.8...13.0.1)

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

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

Author: dependabot[bot]

Sources/Agent/packages.config

@@ -8,7 +8,7 @@
   <package id="Microsoft.Owin.Host.HttpListener" version="2.0.2" targetFramework="net45" />
   <package id="Microsoft.Owin.Hosting" version="2.0.2" targetFramework="net45" />
   <package id="Microsoft.PowerShell.4.ReferenceAssemblies" version="1.0.0" targetFramework="net45" />
-  <package id="Newtonsoft.Json" version="6.0.8" targetFramework="net45" />
+  <package id="Newtonsoft.Json" version="13.0.1" targetFramework="net45" />
   <package id="Owin" version="1.0" targetFramework="net45" />
   <package id="Topshelf" version="3.1.4" targetFramework="net45" />
 </packages>