Docker – “It was not possible to find any compatible framework version” with ASP.NET Core 2.1 in Docker

I'm trying to update an ASP.NET Core 2.0 application that runs in Docker to .NET Core 2.1 RC1.

Here's my simplified .csproj file:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.1</TargetFramework>
    <Version>$(Version)</Version>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.1.0-rc1-final" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.1.0-preview1-final" />
  </ItemGroup>
</Project>

And here's the Dockerfile:

FROM microsoft/dotnet:2.1-sdk-alpine AS builder
WORKDIR /
COPY . .
RUN dotnet restore My.Project/My.Project.csproj
RUN dotnet publish My.Project/My.Project.csproj -o /dockerout/ -c Release

FROM microsoft/dotnet:2.1-aspnetcore-runtime-alpine
WORKDIR /app
EXPOSE 80 5000

COPY --from=builder /dockerout .

ENTRYPOINT ["dotnet", "My.Project.dll"]

I can build the image in Docker but running it fails with

It was not possible to find any compatible framework version The specified framework 'Microsoft.AspNetCore.All', version '2.1.0-rc1-final' was not found.

• Check application dependencies and target a framework version installed at:
  /usr/share/dotnet/
• Installing .NET Core prerequisites might help resolve this problem:
  http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
• The .NET Core framework and SDK can be installed from:
  https://aka.ms/dotnet-download

Is there something I'm missing? Or should I just wait for the final release of Core 2.1?