[Nostromo] Tweak travis and composer

.travis.yml

@@ -6,7 +6,7 @@ php:
   - '7.1'
 
 install:
-  - composer install --prefer-source
+  - composer install
 
 script:
-  - phpunit
+  - vendor/bin/phpunit

composer.json

@@ -16,6 +16,7 @@
     "monolog/monolog": "^1.0",
     "symfony/console": "^3.0",
     "symfony/filesystem": "^3.0",
+    "symfony/event-dispatcher": "^3.0",
     "symfony/finder": "^3.0",
     "symfony/yaml": "^3.0",
     "symfony/process": "^3.0"