Bump Newtonsoft.Json from 10.0.2 to 13.0.1 in /src/GeoJSON.Net.Tests (#162)

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 10.0.2 to 13.0.1.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](JamesNK/Newtonsoft.Json@10.0.2...13.0.1)

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

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src/GeoJSON.Net.Tests/packages.config

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="Newtonsoft.Json" version="10.0.2" targetFramework="net45" />
+  <package id="Newtonsoft.Json" version="13.0.1" targetFramework="net45" />
   <package id="NUnit" version="3.7.0" targetFramework="net461" />
   <package id="NUnit3TestAdapter" version="3.8.0-alpha1" targetFramework="net45" />
 </packages>