Update to require PHP 7.1+#175

WyriHaximus merged 3 commits intoreactphp:3.xreactphp/stream:3.xfrom

WyriHaximus-secret-labs:3.x-raise-minimum-php-version-to-7.1PLUSWyriHaximus-secret-labs/stream:3.x-raise-minimum-php-version-to-7.1PLUSCopy head branch name to clipboard