Set a default content-type for POST & PUT methods, if none was given.

It should also fix #19

@todo[gtl]: split request method

Author: vimishor

lib/Bitbucket/API/Http/Client.php

@@ -182,6 +182,11 @@ public function request($endpoint, $params = array(), $method = 'GET', array $he
             $endpoint .= (strpos($endpoint, '?') === false ? '?' : '&').'format='.$this->getResponseFormat();
         }
 
+        // add a default content-type if none was set
+        if (in_array(strtoupper($method), array('POST', 'PUT')) && empty($headers['Content-Type'])) {
+            $headers['Content-Type'] = 'application/x-www-form-urlencoded';
+        }
+
         $request = $this->createRequest($method, $endpoint);
 
         if (!empty($headers)) {