Update Dockerfile for DotNetCore 3.1 with SonarScanner 5.0.4

Dockerfile

@@ -1,21 +1,18 @@
-FROM mcr.microsoft.com/dotnet/core/sdk:2.2.402
+FROM mcr.microsoft.com/dotnet/core/sdk:3.1.404
 
 # Dockerfile meta-information
 LABEL maintainer="NOS Inovação S.A." \
     app_name="dotnet-sonar"
 
 ENV SONAR_SCANNER_MSBUILD_VERSION=5.0.4.24009 \
-    DOTNETCORE_SDK=2.2.207 \
-    DOTNETCORE_RUNTIME=2.2.8 \
-    NETCOREAPP_VERSION=netcoreapp2.0 \
-    DOCKER_VERSION=5:19.03.13~3-0~debian-stretch \
+    DOTNETCORE_SDK=3.1.404 \
+    DOTNETCORE_RUNTIME=3.1.10 \
+    NETCOREAPP_VERSION=netcoreapp3.0 \
+    DOCKER_VERSION=5:19.03.13~3-0~debian-buster \
     CONTAINERD_VERSION=1.3.7-1 \
     OPENJDK_VERSION=11 \
     NODEJS_VERSION=15
 
-# HACK: OpenJava 11+ is NOT native supported by Debian9
-RUN echo 'deb http://ftp.debian.org/debian stretch-backports main' | tee /etc/apt/sources.list.d/stretch-backports.list
-
 # Linux update
 RUN apt-get update \
     && apt-get dist-upgrade -y \
@@ -29,8 +26,7 @@ RUN apt-get update \
 RUN mkdir -p /usr/share/man/man1mkdir -p /usr/share/man/man1
 
 # Install Java
-RUN apt-get install -y openjdk-$OPENJDK_VERSION-jre \
-    && java -version
+RUN apt-get install -y openjdk-$OPENJDK_VERSION-jre
 
 # Install NodeJs
 RUN wget https://deb.nodesource.com/setup_$NODEJS_VERSION.x \