Update Docker 17.06.0-ce to have multi-stage builds

Author: StefanScherer

appveyor.yml

@@ -4,4 +4,6 @@ image: Visual Studio 2017
 build_script:
   - docker pull microsoft/windowsservercore
   - docker pull microsoft/nanoserver
+  - ps: Install-Package -Name docker -ProviderName DockerMsftProviderInsider -RequiredVersion 17.06.0-ce
+  - ps: start-service docker
   - ps: .\test-build.ps1