* Updated the composer.json to require PHP 7.2, removed Travis CI tests for all PHP versions prior to 7.2 and replace jimdo/prometheus_client_php with endclothing/prometheus_client_php to support PHP 7.2.
* Updated PHPUnit to v8 and Mockery to v1.4 in order to support PHP 7.4.
* Downgraded Mockery from 1.4 to 1.3 in order to support PHP versions < 7.3.