add Symfony 4

Author: andreybolonin

composer.json

@@ -29,11 +29,11 @@
         "phpunit/php-code-coverage": "~4.0||~5.0",
         "behat/behat": "~3.0",
         "guzzlehttp/guzzle": "~6.0",
-        "symfony/config": "~2.3||~3.0",
-        "symfony/dependency-injection": "~2.2||~3.0",
-        "symfony/expression-language": "~2.2||~3.0",
-        "symfony/http-kernel": "~2.3||~3.0",
-        "symfony/http-foundation": "~2.3||~3.0"
+        "symfony/config": "~2.3||~3.0||~4.0",
+        "symfony/dependency-injection": "~2.2||~3.0||~4.0",
+        "symfony/expression-language": "~2.2||~3.0||~4.0",
+        "symfony/http-kernel": "~2.3||~3.0||~4.0",
+        "symfony/http-foundation": "~2.3||~3.0||~4.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~5.0",