Fix some lowest deps

Author: nicolas-grekas

composer.json

@@ -24,7 +24,7 @@
         "symfony/event-dispatcher": "~2.8|~3.0.0",
         "symfony/finder": "~2.0,>=2.0.5|~3.0.0",
         "symfony/http-foundation": "~2.7",
-        "symfony/http-kernel": "~2.7.15|~2.8.8",
+        "symfony/http-kernel": "~2.8.8",
         "symfony/polyfill-mbstring": "~1.0",
         "symfony/filesystem": "~2.3|~3.0.0",
         "symfony/routing": "~2.8|~3.0.0",