Merge pull request #346 from defuse/phpunit

Use composer-provided phpunit

Author: defuse

composer.json

@@ -26,6 +26,7 @@
         "php":  ">=5.4.0"
     },
     "require-dev": {
+        "phpunit/phpunit": "^4|^5",
         "nikic/php-parser": "^2.0|^3.0"
     }
 }