Travis tweaks

.travis.yml

@@ -1,7 +1,19 @@
 language: php
+
 php:
   - 5.3
   - 5.4
   - 5.5
-before_script: composer install
-script: phpunit
+  - hhvm
+
+before_script:
+  - composer self-update
+  - composer install --no-interaction --prefer-source --dev
+
+script:
+  - phpunit
+
+matrix:
+  allow_failures:
+    - php: hhvm
+  fast_finish: true