add php7 to hhvm

.travis.yml

@@ -8,7 +8,7 @@ matrix:
       php: '7.0'
 
     - os: linux
-      php: hhvm-3.12
+      php: hhvm
       env:
         - HHVMPHP7="yes"
 
@@ -27,5 +27,8 @@ install:
   - curl -s http://getcomposer.org/installer | php
   - php composer.phar install --dev --no-interaction --ignore-platform-reqs
 
+before_script:
+  - if [[ $HHVMPHP7 == "yes" ]]; then echo hhvm.php7.all=1 >> /etc/hhvm/php.ini; fi
+
 script:
   - bin/phpunit