Dockerfile change to fix deprecated MAINTAINER line (now LABEL).

Author: geerlingguy

docker/test/Dockerfile

@@ -1,6 +1,6 @@
 # Build an example Docker container image.
 FROM busybox
-MAINTAINER Jeff Geerling <[email protected]>
+LABEL maintainer="Jeff Geerling"
 
 # Run a command when the container starts.
 CMD ["/bin/true"]