reduce max password length on costco.com

[sjbarag]

The rendered password input has maxlength="16", and the "Create Account" page lists "Use between 8 and 16 characters". Decrease the maximum password length.

Overall Checklist

• I agree to the project's Developer Certificate of Origin
• The top-level JSON objects are sorted alphabetically
• There are no open pull requests for the same update

for password-rules.json

• The given rule isn't particularly standard and obvious for password managers
• Generated passwords have been tested from this rule using the Password Rules Validation Tool
• Information has been included about the website's requirements (eg. screenshots, error messages, steps during experimentation, etc.)
• The PR isn't documenting something that would be a common practice among password managers (e.g. minimal length of 6)

Screenshots

[sjbarag]

Thanks @rmondello! 😄