[Docker] Expose a port for the nginx service

Update README.md

Upgrade to Symfony 3.3.5 to fix CVE-2017-11365

hotfix: fix docker configuration

Removed ugly deprecation error in running behat

Fix Travis

Introduce a new file to register filters

Add a Varnish container and enable cache invalidation

Switch to Symfony 3.3 stable

Fix Nginx's config

Revert #224; Upgrade to Docker Compose v3

This reverts commit e7e1ed6b.

Prepare for Symfony 3.3 and API Platform 2.1

Revert "Add PCRE dependency to the docker build for the php image."

Add PCRE dependency to the docker build for the php image.