Update suggested PHP library version

[jeteon]

I recently ran into an issue (https://github.com/crate/crate-pdo/issues/52) which turned out to be due to the documentation suggesting an outdated version. I've corrected the appearances I could find here (https://github.com/crate/crate-web/pull/473) but am having trouble finding the source code which produces this page: https://crate.io/docs/reference/pdo/installation.html . Please update the suggestion library version there too.

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