Update composer.json

Requires php 5.4 due to laravel update

  Problem 1
    - illuminate/support 4.3.x-dev requires php >=5.4.0 -> no matching package found.
    - illuminate/support 4.3.x-dev requires php >=5.4.0 -> no matching package found.
    - Installation request for illuminate/support 4.3.x-dev -> satisfiable by illuminate/support[4.3.x-dev].