Symfony 4 support

Author: yann-eugone

composer.json

@@ -12,10 +12,7 @@
     ],
     "require": {
         "php": ">=5.5.9",
-        "symfony/dependency-injection": "~2.7|~3.0"
-    },
-    "require-dev": {
-        "phpunit/phpunit": "~4.6"
+        "symfony/dependency-injection": "~2.7|~3.0|~4.0"
     },
     "autoload": {
         "psr-4": { "Yokai\\DependencyInjection\\": "src" }