Update CI and docker to new upstream .net core images #65

Looks like Microsoft has restructured their docker hub images of dotnet.

from CI

Build-agent version 1.0.11354-0d3b5199 (2019-05-16T02:00:37+0000)
Docker Engine Version: 18.09.1
Kernel Version: Linux 8c8a2725d557 4.15.0-1035-aws #37-Ubuntu SMP Mon Mar 18 16:15:14 UTC 2019 x86_64 Linux
Starting container microsoft/aspnetcore-build:2.2-stretch
  image cache not found on this host, downloading microsoft/aspnetcore-build:2.2-stretch

Error response from daemon: manifest for microsoft/aspnetcore-build:2.2-stretch not found

from microsoft/aspnetcore-build: Latest images for 2.1 and newer are now available on dotnet/core. See this link for more details about migrating to 2.1.

i think the equivalent would be : microsoft/aspnetcore-build:2.2 -> mcr.microsoft.com/dotnet/core/sdk:2.2

and microsoft/aspnetcore:2.0-stretch -> mcr.microsoft.com/dotnet/core/aspnet:2.2

Where this would need changing:

• The dockerfile: https://github.com/d4software/QueryTree/blob/master/Dockerfile
• The circle ci config: https://github.com/d4software/QueryTree/blob/master/.circleci/config.yml