2.6.0

This release includes the following changes:

• Updated Guzzle to version 6
• Added second factor test mode

Note that Guzzle handles uri's differently in Guzzle 6: trailing slashes are no longer stripped when configuring a base_uri and calling post or get without a specific uri. Parameters should be updated accordingly for the middleware-clientbundle (e.g.: middleware_url_command_api: 'http://mw-dev.stepup.coin.surf.net/app_dev.php/command/' to middleware_url_command_api: 'http://mw-dev.stepup.coin.surf.net/app_dev.php/command').