update the image source

* the image source is changed
* upgrade to 5.0

engine/examples/dotnetcore.md

@@ -44,7 +44,7 @@ tutorial](https://www.asp.net/get-started) to initialize a project or clone our
    the `Dockerfile` to use the DLL file of your project.
 
 ```dockerfile
-FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build-env
+FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build-env
 WORKDIR /app
 
 # Copy csproj and restore as distinct layers
@@ -56,7 +56,7 @@ COPY . ./
 RUN dotnet publish -c Release -o out
 
 # Build runtime image
-FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
+FROM mcr.microsoft.com/dotnet/aspnet:3.1
 WORKDIR /app
 COPY --from=build-env /app/out .
 ENTRYPOINT ["dotnet", "aspnetapp.dll"]
@@ -86,7 +86,7 @@ obj/
     This method is preferred for CI tools like Jenkins, Azure DevOps, GitLab CI, etc. as you can use the same artifacts in multiple deployment models if Docker     isn't the only deployment model being used. Additionally, you'll be able to run unit tests and publish code coverage reports, or use custom plugins on the     artifacts built by the CI.
 
       ```dockerfile
-      FROM mcr.microsoft.com/dotnet/core/aspnet:3.1
+      FROM mcr.microsoft.com/dotnet/aspnet:5.0
       COPY bin/Release/netcoreapp3.1/publish/ App/
       WORKDIR /App
       ENTRYPOINT ["dotnet", "aspnetapp.dll"]
@@ -122,6 +122,6 @@ $ docker run -d -p 8080:80 --name myapp aspnetapp
 ## Further reading
 
   - [ASP.NET Core](https://docs.microsoft.com/aspnet/core/)
-  - [Microsoft ASP.NET Core on Docker Hub](https://hub.docker.com/r/microsoft/dotnet/)
+  - [Microsoft ASP.NET Core on Docker Hub](https://hub.docker.com/_/microsoft-dotnet-sdk/)
   - [Building Docker Images for ASP.NET Core](https://docs.microsoft.com/aspnet/core/host-and-deploy/docker/building-net-docker-images)
   - [Docker Tools for Visual Studio](https://docs.microsoft.com/dotnet/articles/core/docker/visual-studio-tools-for-docker)