Update minimum regex version to fix compile error

[kawasin73]

This is reopened PR of #2717 because I don't have the permission to reopen it.

Even with regex 1.5.1, bindgen fails to build with -Z minimal-versions.

$ cd path/to/rust-bindgen
$ cargo +nightly update -Z minimal-versions
$ cargo build
   Compiling regex-syntax v0.6.24
error[E0433]: failed to resolve: use of undeclared crate or module `unicode_tables`
   --> /home/kawasin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/regex-syntax-0.6.24/src/unicode.rs:351:13
    |
351 |         use unicode_tables::perl_space::WHITE_SPACE;
    |             ^^^^^^^^^^^^^^ use of undeclared crate or module `unicode_tables`

error[E0433]: failed to resolve: use of undeclared crate or module `unicode_tables`
   --> /home/kawasin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/regex-syntax-0.6.24/src/unicode.rs:375:13
    |
375 |         use unicode_tables::perl_decimal::DECIMAL_NUMBER;
    |             ^^^^^^^^^^^^^^ use of undeclared crate or module `unicode_tables`

For more information about this error, try `rustc --explain E0433`.
error: could not compile `regex-syntax` (lib) due to 2 previous errors

---

regex 1.5.3 solves the compile error with unicode-perl feature. https://github.com/rust-lang/regex/blob/master/CHANGELOG.md#153-2021-05-01

Specifing wrong version as the minimum version can cause compile errors on products which depend on bindgen. Minimum versions can be checked with this cargo command.

cargo +nightly update -Z minimal-versions

[kawasin73]

r? @emilio

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[tgross35]

Can you just bump it to the latest version that works for our MSRV? I don’t think there’s any reason to keep such an old version as long as we can build, more bugs have been fixed since #2714 (comment)

[emilio]

It's fine, the lockfile uses a newer one.