edit dockerfile

Dockerfile.dev

@@ -1,11 +1,11 @@
-FROM mcr.microsoft.com/dotnet/core/sdk:3.1 as build-env
+FROM mcr.microsoft.com/dotnet/core/sdk:3 as build-env
 WORKDIR /source
 COPY . .
 RUN dotnet restore --configfile nuget.config --disable-parallel
 RUN dotnet build
 RUN dotnet publish -o /publish --configuration Release;
 
-FROM mcr.microsoft.com/dotnet/aspnet:3.1
+FROM mcr.microsoft.com/dotnet/aspnet:3
 COPY . .
 RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y --no-install-recommends apt-utils
 RUN DEBIAN_FRONTEND=noninteractive apt-get install -y fontconfig