Fix PHP version constraint to match php-jwt v7 requirements

[xeno-suter]

Summary

Follow-up to #64 — firebase/php-jwt was upgraded to ^7.0, but the PHP version constraint was not updated.

Problem

firebase/php-jwt v7 requires PHP >=8.0, but composer.json still declares "php": ">=7.3". This means composer install on PHP 7.x will fail with an unresolvable dependency, which is confusing for users.

See: https://github.com/firebase/php-jwt/blob/main/composer.json

Changes

• composer.json: "php": ">=7.3" → "php": ">=8.0"
• readme.md: PHP requirement updated from 7.4 to 8.0

Why this is safe

• PHP 7.3 EOL: December 2021
• PHP 7.4 EOL: November 2022
• No code changes needed — JWT::encode() API is identical in v7
• firebase/php-jwt v6.x was affected by CVE-2025-45769 (see: GHSA-2x45-7fc3-mxwq)

[D3strukt0r]

Seems my work colleague forgot to notify you, so I might as well do it for him: @maztch

[mirkoRegold]

In JWT version 6 there is a weak encryption, UP for this PR

[D3strukt0r]

i'd also be happy for there to be a release soon, there is no point if this stays in develop forever

[federicoRegold]

UP

[timnijssen]

UP

[MirkoFarina]

@maztch, when will the new version with this fix be released?