Test on PHP 7.3 and 7.4#78

WyriHaximus wants to merge 6 commits intoreactphp:0.2.xreactphp/filesystem:0.2.xfrom

WyriHaximus-secret-labs:travis-php-7.3-and-7.4WyriHaximus-secret-labs/filesystem:travis-php-7.3-and-7.4Copy head branch name to clipboard