Updated composer.json to allow forwards compatiblity with Symfony 2.3

Currently it's not possible to use object-routing in symfony 2.3 projects due to dependency restrictions for the `symfony/property-access` package.

This PR updates the `symfony/property-access` version to ~2.2 which will allow for future versions up to 2.3 to be loaded.

The `composer.lock` file has also been updated to reflect the new changes. The unit tests have been run against both property access v2.2.1 and v2.3.0-RC1 and all passed.