Fix: Use phpunit as installed with Composer

Author: localheinz

.travis.yml

@@ -23,5 +23,8 @@ before_script:
   - git config --global user.email "[email protected]"
   - git config --global user.name "Travis CI"
 
+script:
+  - vendor/bin/phpunit
+
 after_script:
   - php composer/bin/test-reporter