[docs] Fix about page flags

[mbrookes]

Preview: https://deploy-preview-29314--material-ui.netlify.app/about/

[mui-pr-bot]

No bundle size changes

Generated by 🚫 dangerJS against dd74395

[siriwatknp]

👍 Nice.

[michaldudak]

We could store the flags in our repo (it's just a few pngs after all) and not ever worry about another service being down again.

[mnajdova]

We use different URL for the autocomplete countries, maybe we can use the same? https://github.com/mui-org/material-ui/blob/master/docs/src/pages/components/autocomplete/CountrySelect.tsx#L19

[siriwatknp]

We could store the flags in our repo (it's just a few pngs after all) and not ever worry about another service being down again.

I suggest improving it later (maybe in the next quarter). @mbrookes your call.

[oliviertassinari]

Nice to see that we have consolidated on a single flag provider (same as https://deploy-preview-29314--material-ui.netlify.app/components/autocomplete/#country-select). The downside of this one is that the flag aren't squared, it doesn't provide the same visual output, but it's fine 👍

We use different URL for the autocomplete countries, maybe we can use the same? https://github.com/mui-org/material-ui/blob/master/docs/src/pages/components/autocomplete/CountrySelect.tsx#L19

@mnajdova I gave it a try, the png yield icons that don't look as great as the SVG (compression), the png is more efficient for the bandwidth, it's really true when the flag is complex.

We could store the flags in our repo (it's just a few pngs after all) and not ever worry about another service being down again.

I would anticipate this to be more time-consuming than changing the CDN provider every few years.