update .travis.yml for new versions

This removes the testing for Symfony lower then 2.3
as this version is OEL

And adds testing for hhvm

.travis.yml

@@ -1,11 +1,10 @@
 language: php
 
 env:
-    - SYMFONY_VERSION="2.1.*"
-    - SYMFONY_VERSION="2.2.*"
     - SYMFONY_VERSION="2.3.*"
     - SYMFONY_VERSION="2.4.*"
     - SYMFONY_VERSION="2.5.*"
+    - SYMFONY_VERSION="2.6.*"
 
 before_script:
     - COMPOSER_ROOT_VERSION=dev-master
@@ -17,5 +16,12 @@ php:
   - 5.4
   - 5.5
   - 5.6
+  - hhvm
+  - hhvm-nightly
 
 script: phpunit --configuration phpunit.xml.dist --exclude-group ""
+
+matrix:
+    allow_failures:
+        - php: hhvm-nightly
+