Add support for PHP 8

[jhdvc]

It would be great if this extension added support for PHP 8 as it is an actively supported version for almost a year now.

When trying to install the extension in an PHP 8 environment the installation fails while resolving the dependencies in Composer:

# composer require richardhj/contao-ajax_reload_element

# composer update richardhj/contao-ajax_reload_element contao/conflicts

[...]

Problem 1
    - richardhj/contao-ajax_reload_element[v1.0.1, ..., v1.0.3] require richardhj/contao-simple-ajax ~1.0 -> satisfiable by richardhj/contao-simple-ajax[v1.0.0, ..., v1.3.2].
    - richardhj/contao-ajax_reload_element v1.0.0 requires leounglaub/contao-simple-ajax 3.2.x-dev -> satisfiable by richardhj/contao-simple-ajax[v1.0.0, ..., v1.3.2].
    - richardhj/contao-simple-ajax[v1.0.0, ..., v1.2.1] require php ^5.3 || ^7.0 -> your php version (8.0.11.0) does not satisfy that requirement.
    - richardhj/contao-simple-ajax[v1.3.0, ..., v1.3.2] require php ^5.6 || ^7.0 -> your php version (8.0.11.0) does not satisfy that requirement.
    - Root composer.json requires richardhj/contao-ajax_reload_element ^1.0 -> satisfiable by richardhj/contao-ajax_reload_element[v1.0.0, v1.0.1, v1.0.2, v1.0.3].

[richardhj]

That's correct. Please note that the current version is 2.x :-)

[jhdvc]

Yes, version >= 2.1.10 fixed it. Thank you! :-)