Merge pull request MessagePack-CSharp#1452 from neuecc/dependabot/nuget/sandbox/Sandbox/Newtonsoft.Json-13.0.1

Bump Newtonsoft.Json from 10.0.3 to 13.0.1 in /sandbox/Sandbox

Author: AArnott

sandbox/Sandbox/Sandbox.csproj

@@ -9,7 +9,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NETCore.Portable.Compatibility" Version="1.0.1" />
     <PackageReference Include="MsgPack.Cli" Version="0.7.1" />
-    <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
     <PackageReference Include="protobuf-net" Version="2.1.0" />
     <PackageReference Include="ZeroFormatter" Version="1.6.4" />
   </ItemGroup>