minor #136 use HeaderCollection::toArray to fix lowercased header names (jdohuutin)

This PR was squashed before being merged into the 1.0-dev branch (closes #136).

Discussion
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use HeaderCollection::toArray to fix lowercased header names

When creating a Response in Goutte client from a GuzzleResponse, headers names are lowercased.
(location, content-type instead of Location, Content-type).

(see https://github.com/guzzle/guzzle/blob/master/src/Guzzle/Http/Message/Header/HeaderCollection.php#L44)

Rather than use `getAll` method of `HeaderCollection`, we better use [`toArray`](https://github.com/guzzle/guzzle/blob/master/src/Guzzle/Http/Message/Header/HeaderCollection.php#L99).

Commits
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cee172e use HeaderCollection::toArray to fix lowercased header names

Author: fabpot

Goutte/Client.php

@@ -17,7 +17,6 @@
 use Guzzle\Http\Exception\CurlException;
 use Guzzle\Http\Exception\BadResponseException;
 use Guzzle\Http\Message\Response as GuzzleResponse;
-use Guzzle\Http\Message\Header as GuzzleHeader;
 use Guzzle\Http\ClientInterface as GuzzleClientInterface;
 use Guzzle\Http\Client as GuzzleClient;
 use Guzzle\Http\Message\EntityEnclosingRequestInterface;
@@ -181,14 +180,7 @@ protected function addPostFiles($request, array $files, $arrayName = '')
 
     protected function createResponse(GuzzleResponse $response)
     {
-        $headers = $response->getHeaders()->getAll();
-        $headers = array_map(function ($header) {
-            if ($header instanceof GuzzleHeader) {
-                return $header->toArray();
-            }
-
-            return $header;
-        }, $headers);
+        $headers = $response->getHeaders()->toArray();
 
         return new Response($response->getBody(true), $response->getStatusCode(), $headers);
     }