Portfile license attribute with CC0-1.0 license

[Frank Dean]

I am creating a Portfile for a project that uses the Creative Commons
CC0 licence [1].  I have specified the licence in the Portfile as:

    license             CC0-1.0

[1]: https://creativecommons.org/publicdomain/zero/1.0/

Note that the first character after CC is a zero.

When I run `port lint`, I get the following error:

    Error: invalid license 'CC0-1.0': missing hyphen before version
    --->  1 errors and 0 warnings found.

The validation logic in `portlint.tcl` is to split the string on the
hyphen and treat it as invalid, if the last character of the first part
is a digit.

Should I represent the CC0 licence in another way, ignore the error, or
is a fix needed to `portlint.tcl`?

Many thanks,

Frank