Installation through composer failed
I've cloned this repo and then executed `php composer.phar install` command, which returned an error:

```
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
  - Installing symfony/event-dispatcher (v2.3.0)
    Downloading: connection...


  [Composer\Downloader\TransportException]                                                                                       
  The "https://api.github.com/repos/symfony/EventDispatcher/zipball/v2.3.0-RC1" file could not be downloaded (HTTP/1.0 404 Not   
  Found)                                                                                                                         



install [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--no-custom-installers] [--no-scripts] [--no-progress] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader]
```

It seems, that `2.3.0-RC1` tag was removed.
