Upgrade Guzzle

Now, depends on guzzle/guzzle >=3.3.0, <3.9.0.

To upgrade it, change beavior of Adapter\Http\Guzzle.
Now, it returns resource object with header property with an array of
raw array using `$response->getHeaders()->toArray()`.
Add 3.1 and 3.2 to support version of guzzle.
Enable testing with min and max guzzle version.