removed trailing comma in composer.json

Author: gruentee

composer.json

@@ -10,7 +10,7 @@
     "monolog/monolog": "1.19.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "~5.3.4",
+    "phpunit/phpunit": "~5.3.4"
   },
   "autoload": {
     "psr-4":  {"Flowfact\\": "src/Flowfact/"}