Update Dockerfile to use Ubuntu 18.04 LTS and PHP 7.3
Update Dockerfile to use Ubuntu 18.04 LTS and PHP 7.3

zachborboa/php-curl-class,zachborboa/php-curl-class,zachborboa/php-curl-class,php-curl-class/php-curl-class,php-curl-class/php-curl-class,php-curl-class/php-curl-class