Update php-mailjet-v3-simple.class.php

Need to unset 'unique' parameter, otherwise it will not work and you'll get error like this:
stdClass::__set_state(array(
       'ErrorInfo' => '',
       'ErrorMessage' => 'Invalid json input: object ""->"TContactData" has no property "unique"',
       'StatusCode' => 400,
    ))
Merge pull request #16 from vadim-skorba/master

Thanks a lot, this definitely make sense.
Update php-mailjet-v3-simple.class.php