Bump Newtonsoft.Json from 9.0.1 to 13.0.1 in /src/DocNet

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 9.0.1 to 13.0.1.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](https://github.com/JamesNK/Newtonsoft.Json/compare/9.0.1...13.0.1)

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

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

src/DocNet/packages.config

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="Newtonsoft.Json" version="9.0.1" targetFramework="net461" />
+  <package id="Newtonsoft.Json" version="13.0.1" targetFramework="net461" />
   <package id="System.Collections.Immutable" version="1.3.0" targetFramework="net461" />
 </packages>