[TwigBridge] fix lowest version of symfony/form

Author: nicolas-grekas

composer.json

@@ -23,7 +23,7 @@
         "symfony/asset": "~2.8|~3.0|~4.0",
         "symfony/dependency-injection": "~2.8|~3.0|~4.0",
         "symfony/finder": "~2.8|~3.0|~4.0",
-        "symfony/form": "^3.4.13|~4.0.13|^4.1.2",
+        "symfony/form": "^3.4.16|~4.0.13|^4.1.5",
         "symfony/http-foundation": "^3.3.11|~4.0",
         "symfony/http-kernel": "~3.2|~4.0",
         "symfony/polyfill-intl-icu": "~1.0",