Update dependencies constraints

Author: roissard

composer.json

@@ -30,14 +30,14 @@
   },
   "require": {
     "php": ">=5.6",
-    "symfony/finder": "^2.7|^3.0",
+    "symfony/finder": "^2.7|^3.0|^4.0",
     "voryx/thruway": "~0.5",
-    "symfony/serializer": "^2.7|^3.0",
+    "symfony/serializer": "^2.7|^3.0|^4.0",
     "react/child-process": "~0.4",
-    "symfony/event-dispatcher": "^2.7|^3.0"
+    "symfony/event-dispatcher": "^2.7|^3.0|^4.0"
   },
   "require-dev": {
-    "symfony/symfony": "^2.7|^3.0",
+    "symfony/symfony": "^2.7|^3.0|^4.0",
     "doctrine/orm": "~2.1",
     "symfony/yaml": "2.*",
     "phpunit/phpunit": "~5.0"