Revert changes to composer.json and composer.lock

Note that this commit depends on a pull request for gitter, and is
therefore in an untestable state after reverting composer.json.
Its predecessor should be testable, however.

composer.json

@@ -8,8 +8,7 @@
     },
     "require-dev": {
         "symfony/browser-kit": "2.1.*",
-        "symfony/css-selector": "2.1.*",
-        "phpunit/phpunit": "3.7.*"
+        "symfony/css-selector": "2.1.*"
     },
     "minimum-stability": "dev",
     "autoload": {