#115 - Update docker images to v3.1.

docker/Dockerfile.api-stretch-slim-arm32v7

@@ -1,12 +1,12 @@
 # Build sources.
-FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build
+FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
 WORKDIR /src
 COPY . ./
 WORKDIR /src/src/Recollections.Api
 RUN dotnet publish -c Release -r linux-arm -o /app
 
 # Final image.
-FROM neptuo/aspnet-system-drawing:2.2-stretch-slim-arm32v7
+FROM neptuo/aspnet-system-drawing:3.1-buster-slim-arm32v7
 WORKDIR /app
 COPY --from=build /app .
 ENTRYPOINT ["./Recollections.Api"]

docker/Dockerfile.aspnet-system-drawing-deps-stretch-slim-arm32v7

@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/dotnet/core/aspnet:2.2-stretch-slim-arm32v7
+FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim-arm32v7
 RUN apt-get update \
     && apt-get install -y --allow-unauthenticated \
         libc6-dev \