exclude Symfony 3.0 from Composer deps

composer.json

@@ -18,28 +18,28 @@
     "require": {
         "php": ">=5.3.3",
         "pimple/pimple": "~1.0",
-        "symfony/event-dispatcher": "~2.3",
-        "symfony/http-foundation": "~2.3",
-        "symfony/http-kernel": "~2.3",
-        "symfony/routing": "~2.3"
+        "symfony/event-dispatcher": "~2.3,<3.0",
+        "symfony/http-foundation": "~2.3,<3.0",
+        "symfony/http-kernel": "~2.3,<3.0",
+        "symfony/routing": "~2.3,<3.0"
     },
     "require-dev": {
-        "symfony/security": "~2.3",
-        "symfony/config": "~2.3",
-        "symfony/locale": "~2.3",
-        "symfony/form": "~2.3",
-        "symfony/browser-kit": "~2.3",
-        "symfony/css-selector": "~2.3",
-        "symfony/debug": "~2.3",
-        "symfony/dom-crawler": "~2.3",
-        "symfony/finder": "~2.3",
-        "symfony/monolog-bridge": "~2.3",
-        "symfony/options-resolver": "~2.3",
-        "symfony/process": "~2.3",
-        "symfony/serializer": "~2.3",
-        "symfony/translation": "~2.3",
-        "symfony/twig-bridge": "~2.3",
-        "symfony/validator": "~2.3",
+        "symfony/security": "~2.3,<3.0",
+        "symfony/config": "~2.3,<3.0",
+        "symfony/locale": "~2.3,<3.0",
+        "symfony/form": "~2.3,<3.0",
+        "symfony/browser-kit": "~2.3,<3.0",
+        "symfony/css-selector": "~2.3,<3.0",
+        "symfony/debug": "~2.3,<3.0",
+        "symfony/dom-crawler": "~2.3,<3.0",
+        "symfony/finder": "~2.3,<3.0",
+        "symfony/monolog-bridge": "~2.3,<3.0",
+        "symfony/options-resolver": "~2.3,<3.0",
+        "symfony/process": "~2.3,<3.0",
+        "symfony/serializer": "~2.3,<3.0",
+        "symfony/translation": "~2.3,<3.0",
+        "symfony/twig-bridge": "~2.3,<3.0",
+        "symfony/validator": "~2.3,<3.0",
         "twig/twig": ">=1.8.0,<2.0-dev",
         "doctrine/dbal": "~2.2",
         "swiftmailer/swiftmailer": "5.*",