fix detecting php.ini location on HHVM builds

Now, let's also make sure that HHVM builds do not fail anymore in the
future without us noticing that.

.travis.yml

@@ -12,8 +12,6 @@ env:
 
 matrix:
   fast_finish: true
-  allow_failures:
-    - php: hhvm
   include:
     - php: 5.3
       env: deps="low"
@@ -29,7 +27,8 @@ matrix:
     - php: hhvm
 
 before_install:
-  - echo memory_limit = -1 >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
+  - if [ "$TRAVIS_PHP_VERSION" == "hhvm" ]; then INI_FILE=/etc/hhvm/php.ini; else INI_FILE=~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini; fi
+  - echo memory_limit = -1 >> $INI_FILE
   - if [ "$COVERAGE" != "yes" -a "$TRAVIS_PHP_VERSION" != "hhvm" ]; then phpenv config-rm xdebug.ini; fi
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require symfony/symfony:${SYMFONY_VERSION} --dev --no-update; fi