change the version of symfony/* to ~2.7 #5

And also the version of `php` is changed to `>=5.3.9`

.travis.yml

@@ -1,7 +1,6 @@
 language: php
 
 php:
-  - 5.3.3
   - 5.3
   - 5.4
   - 5.5

composer.json

@@ -11,21 +11,21 @@
         }
     ],
     "require": {
-        "php": ">=5.3.3",
-        "symfony/config": "~2.3",
-        "symfony/dependency-injection": "~2.3",
-        "symfony/framework-bundle": "~2.3",
-        "symfony/http-kernel": "~2.3",
-        "symfony/routing": "~2.3"
+        "php": ">=5.3.9",
+        "symfony/config": "~2.7",
+        "symfony/dependency-injection": "~2.7",
+        "symfony/framework-bundle": "~2.7",
+        "symfony/http-kernel": "~2.7",
+        "symfony/routing": "~2.7"
     },
     "require-dev": {
         "phpunit/phpunit": "~4.0",
         "piece/stagehand-testrunner": "~4.1@dev",
-        "symfony/browser-kit": "~2.3",
-        "symfony/filesystem": "~2.3",
-        "symfony/http-foundation": "~2.3",
+        "symfony/browser-kit": "~2.7",
+        "symfony/filesystem": "~2.7",
+        "symfony/http-foundation": "~2.7",
         "symfony/twig-bridge": "~2.7",
-        "symfony/twig-bundle": "~2.3"
+        "symfony/twig-bundle": "~2.7"
     },
     "autoload": {
         "psr-4": {