Update the Dockerfile MAINTAINED instruction. (MicrosoftDocs#842)

The MAINTAINED instruction is deprecated. It's preferred that you use the LABEL instruction to set a label for maintainer. This allows the information to be obtained via "docker inspect" and to be filtered using "-f".

virtualization/windowscontainers/manage-docker/manage-windows-dockerfile.md

@@ -44,7 +44,7 @@ In its most basic form, a Dockerfile can be very simple. The following example c
 FROM microsoft/windowsservercore
 
 # Metadata indicating an image maintainer.
-MAINTAINER [email protected]
+LABEL maintainer="[email protected]"
 
 # Uses dism.exe to install the IIS role.
 RUN dism.exe /online /enable-feature /all /featurename:iis-webserver /NoRestart