Your requirements could not be resolved to an installable set of packages.
Your requirements could not be resolved to an installable set of packages. Error: Problem 1 - Installation request for magento/product-community-edition 2.2.3 -> satisfiable by magento/product-community-edition[2.2.3]. - magento/product-community-edition 2.2.3 requires php 7.0.2|7.0.4|~7.0.6|~7.1.0 -> your PHP version (5.4.16) does not satisfy that requirement. Problem 2 - Installation request for squizlabs/php_codesniffer 3.2.2 -> satisfiable by squizlabs/php_codesniffer[3.2.2]. - squizlabs/php_codesniffer 3.2.2 requires ext-xmlwriter * -> the requested PHP extension xmlwriter is missing from your system. Problem 3 - phpunit/phpunit 6.2.4 requires php ^7.0 -> your PHP version (5.4.16) does not satisfy that requirement. - phpunit/phpunit 6.2.3 requires php ^7.0 -> your PHP version (5.4.16) does not satisfy that requirement. - phpunit/phpu...