Fails to parse `Changes` entries with slash-separated datestamps

[leonerd]

A Changes entry thus is parsed correctly:

0.09    2017-08-13 17:44:48
        [CHANGES]
        ...

But using slashes instead of hyphens as previously used, was not:

0.08    2017/08/10 16:48:52
        [CHANGES]
        ...

I'm aware the latter isn't strictly valid under ISO8601, but I wonder if a small exception could be allowed in this common use-case.

(These examples can be seen at https://metacpan.org/release/PEVANS/Future-AsyncAwait-0.09 vs https://metacpan.org/release/PEVANS/Future-AsyncAwait-0.08)