[2.8] Fix lowest deps

Author: nicolas-grekas

composer.json

@@ -20,11 +20,11 @@
         "symfony/asset": "~2.7|~3.0.0",
         "symfony/dependency-injection" : "~2.8",
         "symfony/config" : "~2.4",
-        "symfony/event-dispatcher": "~2.5|~3.0.0",
+        "symfony/event-dispatcher": "~2.8|~3.0.0",
         "symfony/http-foundation": "~2.4.9|~2.5,>=2.5.4|~3.0.0",
         "symfony/http-kernel": "~2.7|~3.0.0",
         "symfony/filesystem": "~2.3|~3.0.0",
-        "symfony/routing": "~2.6,>2.6.4|~3.0.0",
+        "symfony/routing": "~2.8|~3.0.0",
         "symfony/security-core": "~2.6|~3.0.0",
         "symfony/security-csrf": "~2.6|~3.0.0",
         "symfony/stopwatch": "~2.3|~3.0.0",