Update NuGet.Packaging to version 6.2.1 (#733)

* updat NuGet.Packaging to version 6.2.1 which depends on Newtonsoft 13.0.1 or higher

* update other NuGet package versions

Author: anamnavi

src/code/PowerShellGet.csproj

@@ -15,12 +15,12 @@
   <ItemGroup>
     <PackageReference Include="LinqKit.Core" Version="1.1.17" />
     <PackageReference Include="morelinq" Version="3.3.2" />
-    <PackageReference Include="NuGet.Commands" Version="5.11.2" />
-    <PackageReference Include="NuGet.Common" Version="5.11.2" />
-    <PackageReference Include="NuGet.Configuration" Version="5.11.2" />
-    <PackageReference Include="NuGet.Packaging" Version="5.11.2" />
-    <PackageReference Include="NuGet.ProjectModel" Version="5.11.2" />
-    <PackageReference Include="NuGet.Protocol" Version="5.11.2" />
+    <PackageReference Include="NuGet.Commands" Version="6.2.1" />
+    <PackageReference Include="NuGet.Common" Version="6.2.1" />
+    <PackageReference Include="NuGet.Configuration" Version="6.2.1" />
+    <PackageReference Include="NuGet.Packaging" Version="6.2.1" />
+    <PackageReference Include="NuGet.ProjectModel" Version="6.2.1" />
+    <PackageReference Include="NuGet.Protocol" Version="6.2.1" />
     <PackageReference Include="NuGet.Repositories" Version="4.3.0-beta1-2418" />
     <PackageReference Include="PowerShellStandard.Library" Version="7.0.0-preview.1" />
     <PackageReference Include="System.Data.DataSetExtensions" Version="4.6.0-preview3.19128.7" />