Fix FROM directive
Fix FROM directive

It’s SUPPOSED to be a colon.

> Supported **tags** and respective Dockerfile links
> 12.04.5, 12.04, precise-20151208, precise (precise/Dockerfile)
> 14.04.3, 14.04, trusty-20151208, trusty, latest (trusty/Dockerfile)

as per: https://hub.docker.com/_/ubuntu/

briandk/ubuntu-trusty