Update composer.json

Author: api-postcode

composer.json

@@ -17,8 +17,7 @@
         "api-postcode/php-client": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.0",
-        "matthiasnoback/symfony-dependency-injection-test": "^2.0"
+        "phpunit/phpunit": "^6.0"
     },
     "autoload": {
         "psr-4": {