validate_verification_code() now requires a string instead of an int in v25

[dannyoleson]

Validation stopped working for me in v24. I was always getting an invalid verification code response. I saw in the changelog that there were changes to this code, so I updated and tried again, at which point I got a syntax error when trying validation again. I passed the code in as a string, and then it succeeded. If this interface change was expected, the documentation should be updated. Otherwise, the function should be fixed.