do not depend on a fixed date in layout tests

By default, the `DateType` as well as the `DateTimeType` set the choices
being available for the year to a range starting five years in the past.
After some time, this will make tests fail when the year of the fixed
date being used as the initial data is before the first year being part
of the choices.

Author: xabbuh

composer.json

@@ -40,7 +40,7 @@
         "symfony/dom-crawler": "~2.0,>=2.0.5",
         "symfony/intl": "~2.3",
         "symfony/security": "~2.6",
-        "symfony/form": "~2.7,>=2.7.2",
+        "symfony/form": "~2.7.23|~2.8.16",
         "symfony/class-loader": "~2.1",
         "symfony/expression-language": "~2.6",
         "symfony/process": "~2.0,>=2.0.5",