use matthiasnoback/symfony-config-test dev-master as 3.1

Author: fbourigault

composer.json

@@ -38,6 +38,7 @@
     "require-dev": {
         "guzzlehttp/psr7": "^1.0",
         "matthiasnoback/symfony-dependency-injection-test": "^1.1 || ^2.0 || dev-feature/symfony-4",
+        "matthiasnoback/symfony-config-test": "^2.0 || dev-master as 3.1",
         "nyholm/nsa": "^1.1",
         "php-http/buzz-adapter": "^0.3",
         "php-http/curl-client": "^1.0",