update dom-crawler version (#20)

Author: ctf0

composer.json

@@ -20,8 +20,8 @@
         "php" : "^5.5|^7.0",
         "illuminate/support": "^5.3",
         "illuminate/http": "^5.3",
-        "symfony/dom-crawler": "^2.7|^3.0",
-        "symfony/css-selector": "^2.7|^3.0"
+        "symfony/dom-crawler": "^2.7|^3.0|^4.0",
+        "symfony/css-selector": "^2.7|^3.0|^4.0"
     },
     "require-dev": {
         "phpunit/phpunit" : "^4.0|^5.0",