PHP 8 compatibility

Hi,

as you will know, PHP 7.4 will reach its “end of life” in late November. A rough test on a sandbox instance indicates that this extension should be compatible, were it not for a single line in the boiler plate code generated by an earlier version of civix, which uses curly braces to access an array element. This merge request changes that line. Could you merge it? Even if there are more issues I overlooked, this will at least make it easier to find them. So could you merge this pull request and maybe publish a new version? Thanks.