Move to new travis containerised infrastructure

.travis.yml

@@ -1,4 +1,11 @@
-language: php 
+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