Format the credit card month and year as said in the Merchnat Warrior do...

Format the credit card month and year as said in the Merchnat Warrior documentation.

### API Method - addCard
[Link](http://dox.merchantwarrior.com/files/MWE%20API.pdf)

**cardExpiryMonth**
Example: 05
Notes: This must be in MM format. The month must be zero-padded if it’s less than 10. 
Valid Length: 2 digits.

**cardExpiryYear**
Example: 13
Notes: This must be in YY format.
Valid Length: 2 digits