Credit card expiration field doesn't ignore the / character

[crenshaw-dev]

- Do you want to request a feature or report a bug?

Bug.

- What is the current behavior?

The credit card expiration field does not filter out the / character.

- If the current behavior is a bug, please provide the steps to reproduce.

Go the the membership page, click any "sign up" link, type the / character in the credit card expiration field.

- What is the expected behavior?

The field should ignore the / character.

- Please mention your operating system version and the version of your browser

I'm using Windows 10 with Chrome 62.