Package is not compatible with PHP 7.4.1

[MegaThorx]

They bumped the version of ext-json from 1.5 to 7.4.1. It works fine with PHP 7.3

  Problem 1
    - multitheftauto/mtasa-php-sdk 1.0.2 requires ext-json ^1.5 -> the requested PHP extension json has the wrong version (7.4.1) installed.
    - multitheftauto/mtasa-php-sdk 1.0.2 requires ext-json ^1.5 -> the requested PHP extension json has the wrong version (7.4.1) installed.
    - Installation request for multitheftauto/mtasa-php-sdk 1.0.2 -> satisfiable by multitheftauto/mtasa-php-sdk[1.0.2].

/EDIT php/php-src#4459

[ecastro98]

Thanks for the issue! Sorry for the little delay :P