Use PHPUnit 4

Christoph Singer · Christoph Singer · commit dc806bfd92d0 · 2018-03-08T17:17:50.000+01:00
diff --git a/composer.json b/composer.json
@@ -17,7 +17,7 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "^5.0"
+        "phpunit/phpunit": "^4.0"
     }
 }
 
