Update this repository to version 0.0.39 of cybersource-rest-client-php

[Mutahhar]

Hello,

I would like to bring to your attention that the cybersource-rest-samples-php repository is currently using version 0.0.38 of the cybersource-rest-client-php. However, the latest version of the cybersource-rest-client-php is now updated to 0.0.39.

This has caused some issues with the cybersource-rest-samples-php repository, as some files have been deleted from the cybersource-rest-client-php. For instance, the CyberSource\Api\KeyGenerationApi has been removed from version 0.0.39, but it is still referenced in the cybersource-rest-samples-php repository (see here).

Therefore, I kindly request that you update the cybersource-rest-samples-php repository to version 0.0.39 of the cybersource-rest-client-php.