Update common Docker engineering infrastructure with latest (dotnet#213)

Author: dotnet-maestro-bot

eng/common/templates/variables/docker-images.yml

@@ -1,6 +1,6 @@
 variables:
-  imageNames.imageBuilder.linux: mcr.microsoft.com/dotnet-buildtools/image-builder:debian-20191122151918
-  imageNames.imageBuilder.windows: mcr.microsoft.com/dotnet-buildtools/image-builder:nanoserver-20191122151918
+  imageNames.imageBuilder.linux: mcr.microsoft.com/dotnet-buildtools/image-builder:debian-20191211140647
+  imageNames.imageBuilder.windows: mcr.microsoft.com/dotnet-buildtools/image-builder:nanoserver-20191211140647
   imageNames.imageBuilder.withrepo: imagebuilder-withrepo:$(Build.BuildId)-$(System.JobId)
   imageNames.testRunner: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-stretch-slim-docker-testrunner-d61254f-20190807161111
   imageNames.testRunner.withrepo: testrunner-withrepo:$(Build.BuildId)-$(System.JobId)