Update SDK to use guzzle 3.*

If you look b65b2a9543fc2954943426126abea7bed3f06483 The *alchemy-fr/Phraseanet-PHP-SDK-Silex-Provider* has been updated to use Guzzle 3.* **but do not precise the requirement of guzzle >3.0 in the composer.json** https://github.com/alchemy-fr/Phraseanet-PHP-SDK-Silex-Provider/blob/master/composer.json and if you look cf7e53bc97f89edc4d25328ee3fce4246ee7135b The *alchemy-fr/Phraseanet-PHP-SDK* has been updated to use >=2.7,<3.0.

So when you use both of them and update dependencies there is no error,  but you can not no longer use the *alchemy-fr/Phraseanet-PHP-SDK-Silex-Provider* because it is not able to work with guzzle <3.0.

So I've updated  *alchemy-fr/Phraseanet-PHP-SDK* to use at least guzzle 3.0 and will a do a PR to require guzzle >3.0 dependency in the  *alchemy-fr/Phraseanet-PHP-SDK-Silex-Provider* when this PR will be merged because it require  *alchemy-fr/Phraseanet-PHP-SDK* to use Guzzle >3.0