Synchronize .travis.yml with upstream moodle-plugin-ci, fix broken Behat tests.

.travis.yml

 language: php
 
-sudo: true
-
 addons:
-  chrome: stable
   postgresql: "9.4"
-  apt:
-    packages:
-      - openjdk-8-jre-headless
-      - chromium-chromedriver
 
 services:
   - mysql
   - postgresql
+  - docker
 
 cache:
   directories:
@@ -38,7 +32,7 @@ before_install:
   - cd ../..
   - composer create-project -n --no-dev --prefer-dist blackboard-open-source/moodle-plugin-ci ci dev-master
   - export PATH="$(cd ci/bin; pwd):$(cd ci/vendor/bin; pwd):$PATH"
-  - google-chrome-stable --headless --disable-gpu --remote-debugging-port=9222 http://127.0.0.1 &
+  - docker run -d -p 127.0.0.1:4444:4444 --net=host -v /dev/shm:/dev/shm selenium/standalone-chrome:3
 
 install:
   - moodle-plugin-ci install