Remove deprecated MAINTAINER instruction from Dockerfile
Remove deprecated MAINTAINER instruction from Dockerfile

Deprecated in Docker Release v1.13.0:
https://github.com/docker/cli/blob/master/docs/deprecated.md#maintainer-in-dockerfile

Replace it with `LABEL <key>=<value>` instruction and set as
maintainer the analytics@skroutz.gr email.

skroutz/analytics.js,skroutz/analytics.js,skroutz/analytics.js