Use Json.Net 9.x to make roslyn happy

Author: Redth

Cake.Json.Tests/Cake.Json.Tests.csproj

@@ -37,7 +37,7 @@
       <Version>0.22.0</Version>
     </PackageReference>
     <PackageReference Include="Newtonsoft.Json">
-      <Version>10.0.3</Version>
+      <Version>9.0.1</Version>
     </PackageReference>
     <PackageReference Include="NUnit">
       <Version>3.8.1</Version>

Cake.Json/Cake.Json.csproj

@@ -22,11 +22,11 @@
   <ItemGroup>
     <PackageReference Include="Cake.Core" Version="0.22.0" />
     <PackageReference Include="Cake.Common" Version="0.22.0" />
-    <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />
+    <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Properties\" />
+  <ItemGroup>
+    <Folder Include="Properties\" />
   </ItemGroup>
 
 </Project>