Remove support for deprecated dependencies

[jdecool]

Actually the bundle ensure compatibility with PHP 5.3+ and Symfony 2.3+.

But PHP 5.3 is unmaintened since august 2014, 5.4 since september 2015, 5.5 since july 2016 and 5.6 now only have security fixes.

It's the same for Symfony framework, only 2.7, 2.8 and 3.1+ are currently maintened.

I propose to drop support of all unmaintened dependencies for the next releases.

[Chinachengjiajia]

很久没用过PHP 5.3了，我们这边都是用的高版本的PHP Symfony 这个东西好用吗？