Use PHPUnit config file correctly in Travis.

Author: Felix Arntz

.travis.yml

@@ -82,7 +82,7 @@ before_script:
     nvm install 8
   - npm install
 script:
-  - phpunit
+  - phpunit -c phpunit.xml.dist
   - |
     if [[ "$TRAVIS_PHP_VERSION" != "5.2" ]]; then
       npm test