[Tests] Restricted doctrine/dbal to versions <2.10.0

The 2.10.0 release of doctrine/dbal introduced strict return types
on e.g. QueryBuilder. Unfortunately old PHPUnit 4.8.x can't handle
mocking of such classes properly.

composer.json

@@ -36,6 +36,7 @@
         "twig/twig": "~1.35|~2.4"
     },
     "require-dev": {
+        "doctrine/dbal": "<2.10.0",
         "friendsofphp/php-cs-fixer": "2.15.3",
         "phpunit/phpunit": "^4.8.35",
         "matthiasnoback/symfony-dependency-injection-test": "~0.7.6",