Update flexbox.json for Safari bugs

[aardrian]

Added information about Safari/iOS issues with tables that use display:flex. Includes link to Safari bug https://bugs.webkit.org/show_bug.cgi?id=257458.

[jensimmons]

It's a great idea to mark Flexbox with this bug. But I disagree with downgrading Flexbox as a whole as "partially supported". The bug only affects tables that have display: flex on the <tr>s.

Layout out HTML tables using Flexbox is not a core usecase.

Let's include the footnote, but leave the level of support.

[aardrian]

It's a great idea to mark Flexbox with this bug. But I disagree with downgrading Flexbox as a whole as "partially supported". The bug only affects tables that have display: flex on the s.

I feel "only" is doing a lot of work there considering I found this because of a banking client using it this way (and another client considering it until I flagged it).

Given my small set of clients, I can only assume (perhaps poorly) it was more pervasive in non-public data table uses (where lots of financial data appears).