Add support for JCB and Diners Club cards.

According to the [documentation](https://support.balancedpayments.com/hc/en-us/articles/200319895-Does-Balanced-accept-JCB-and-Diners-Club-cards) Balanced supports JCB and Diners, but they weren't recognized by balanced-js. Added using
test card numbers found elsewhere online; these should be changed if there are specific numbers
you support.
Merge pull request #68 from zachsnow/dev/more-credit-card-types

Add support for JCB and Diners Club cards.