[FIX] Updated JSON request format

Fixed: "`call_method': Got error from Yandex API, error code: 9 | This
field must be an array (The Logins field must be an array)." Passing
‘param’ single-string array instead of ‘login’ string to match Version
4 API specs: http://api.yandex.com/direct/doc/concepts/JSON.xml.