This is a minor release, with the main change being the use of phpunit 8.0
 * Upgraded to PHPUnit 8.0
 * Fixed tests that used assertInternalType to use the appropriate replacements.
 * Allows composer installation on PHP ^8.0 versions
 * Adds an explicit Travis CI build for PHP 7.4, now that PHP 8.x is PHP nightly
 * Mark PHP 7.4 and nightly builds as allowed_failures.