Fix expired test cards

[varyonic]

AIM tests were using a card expiry date in 2018. Fix from happening again.

[varyonic]

The AIM::Transaction MD5 hash specs pass for me locally when I update md5_value in credentials.yml to match the value in the settings for my sandbox account. It appears to me that Travis is using hard coded values where the md5_value does not match. Possible fixes:

• Update the account settings of the hard-coded test account to match
• Mark the two tests as 'pending' and ignore them
• Allow the contents of credentials.yml to be overridden by environment variables in Travis CI and provide the correct md5_value with an environment variable. I would consider this the best practice: let me know if you would like a PR for that.