Fix a unicode error in CyberSource2

This is the same fix that @dianakhuang made to the original CC implementation in this commit: https://github.com/edx/edx-platform/commit/3b668522

@dianakhuang @stephensanchez Please review.  I think we will need to hotfix this and will coordinate with ops.

[ECOM-291](https://openedx.atlassian.net/browse/ECOM-291)