[DOCKER] Update the documentation links.

docker/firefox_docker/Dockerfile

+# documentation link: https://docs.docker.com/engine/installation/linux/ubuntu/
+
 FROM ubuntu:14.04
 
 RUN apt-get update && apt-get install -y firefox

docker/lmgc_docker/Dockerfile

-# documentation link: https://docs.docker.com/engine/installation/linux/ubuntulinux/
+# documentation link: https://docs.docker.com/engine/installation/linux/ubuntu/
 
 # Docker to get the latest release of LMGC90
 FROM ubuntu:14.04

docker/lmgc_n_paraview_docker/Dockerfile

+# documentation link: https://docs.docker.com/engine/installation/linux/ubuntu/
 # documentation link: http://stackoverflow.com/questions/24095968/docker-for-gui-based-environments
 
 # Docker to get the latest release of LMGC90

docker/paraview_docker/Dockerfile

+# documentation link: https://docs.docker.com/engine/installation/linux/ubuntu/
 # Documentation link: http://fabiorehm.com/blog/2014/09/11/running-gui-apps-with-docker/
+
 FROM ubuntu:14.04
 
 RUN apt-get update && apt-get install -y python-vtk paraview dbus-x11