updated composr to match symfony 3 (#33)

Author: wachterjohannes

composer.json

@@ -12,10 +12,10 @@
     "require": {
         "php": "~5.5 || ~7.0",
         "php-task/php-task": "dev-master",
-        "symfony/http-kernel": "^2.6",
-        "symfony/dependency-injection": "^2.6",
-        "symfony/config": "^2.6",
-        "symfony/console": "^2.6",
+        "symfony/http-kernel": "^2.6 || ^3.0",
+        "symfony/dependency-injection": "^2.6 || ^3.0",
+        "symfony/config": "^2.6 || ^3.0",
+        "symfony/console": "^2.6 || ^3.0",
         "doctrine/orm": "^2.5"
     },
     "require-dev": {