Update composer.json

[amadrocky]

Modification of the minimum version required for the "mailjet/mailjet-apiv3-php" bundle because in the "MailjetClient" class on the "master" branch we end up with an error "Warning: Declaration of Mailjet\MailjetBundle\Client\MailjetClient::post(array $resource, array $args = Array, array $options = Array): Mailjet\Response should be compatible with Mailjet\Client::post($resource, array $args = Array, array $options = Array)" because some types are missing.