Move to new travis containerised infrastructure

.travis.yml

@@ -1,5 +1,12 @@
 language: php
 
+sudo: false
+
+addons:
+  apt:
+    packages:
+      - tidy
+
 php:
   - 5.4
 
@@ -32,9 +39,6 @@ matrix:
       env: DB=MYSQL
     - php: hhvm-nightly
       env: DB=MYSQL
-      before_install:
-        - sudo apt-get update -qq
-        - sudo apt-get install -y tidy
 
 before_script:
  - composer self-update || true