Use microsoft-provided docker images

Dockerfile

@@ -1,23 +1,7 @@
-FROM debian:testing-slim as builder
+FROM mcr.microsoft.com/dotnet/core/sdk as builder
 
 ENV DOTNET_CLI_TELEMETRY_OPTOUT 1
 
-RUN apt-get update \
-    && apt-get -y install \
-        git \
-        gnupg2 \
-        wget \
-    && wget -qO- https://packages.microsoft.com/keys/microsoft.asc | apt-key add - \
-    && wget -qO /etc/apt/sources.list.d/microsoft.list https://packages.microsoft.com/config/debian/10/prod.list \
-    && apt-get -y purge \
-        gnupg2 \
-        wget \
-    && apt-get update \
-    && apt-get -y install \
-        dotnet-sdk-3.0 \
-    && apt-get -y autoremove --purge \
-    && rm -rf /var/lib/apt/lists/*
-
 ARG CACHEBUST=1
 ARG GIT_COMMIT=master
 ARG CONFIGURATION=Release
@@ -27,11 +11,10 @@ RUN git clone --depth=50 https://github.com/ppy/osu \
     && git checkout ${GIT_COMMIT} \
     && dotnet publish -c ${CONFIGURATION} -r linux-x64 --self-contained true -o /opt/osu/ osu.Desktop
 
-FROM debian:testing-slim
+FROM mcr.microsoft.com/dotnet/core/runtime-deps
 
 RUN apt-get update \
     && apt-get -y install --no-install-recommends \
-        ca-certificates \
         ffmpeg \
         libgl1 \
         pulseaudio \