Declare exceptions as final #342
Description
In #300 and #310 I've missed out to set the new exeptions to final. Doing this now would be a breaking change and will therefore be done in v3.0.0.
\Redmine\Exception\ClientException\Redmine\Exception\InvalidApiNameException\Redmine\Exception\InvalidParameterException\Redmine\Exception\MissingParameterException\Redmine\Exception\SerializerException