Revert change to Newtonsoft.Json version

Author: cormacpayne

src/Dependencies.Test.Netcore.targets

@@ -13,7 +13,7 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0" />
-    <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />
+    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp2.1'">
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />