fix hhvm build

Author: lsmith77

.travis.yml

@@ -23,7 +23,7 @@ matrix:
 
 before_script:
   - composer self-update
-  - echo 'memory_limit = -1' >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
+  - sh -c 'if [ "${TRAVIS_PHP_VERSION}" != "hhvm" ]; then echo "memory_limit = -1" >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini; fi;'
   - composer require symfony/symfony:${SYMFONY_VERSION}
   - vendor/symfony-cmf/testing/bin/travis/phpcr_odm_doctrine_dbal.sh