.net core project stripped of all references #2518

Description

The .csproj file for a .net core project is not updated with any references either during a nuget conversion or when adding a package.

Repro steps

Please provide the steps required to reproduce the problem

1. Create a new ASP.NET Core project in Visual Studio
2. Add the paket bootstrap at the solution level
3. In the project directory run .paket/paket.exe convert-from-nuget
4. Attempt to build in Visual Studio

https://github.com/stimms/PaketReferenceBug

Expected behaviour

Project references the packages listed as dependencies.

Actual behaviour

The project has no references to any libraries and cannot be built.

Known workarounds

No trivial workaround