It is better to use guzzle/guzzle through a bundle if you are using symfony.
I recommend you to use misd/guzzle-bundle. So, add this line on your composer.json
"misd/guzzle-bundle": "1.1.*@dev"
Then, update your bundles:
php composer.phar update
And you will get the last version of guzzle/guzzle.
Dont forget to install this:
sudo apt-get install php5-curl