Use latest composer

Author: kristof-ringleff

magento-coding-standard/Dockerfile

@@ -1,6 +1,6 @@
 FROM php:7.3-cli-alpine3.9
 
-COPY --from=composer:1.9.1 /usr/bin/composer /usr/local/bin/composer
+COPY --from=composer:1.9.3 /usr/bin/composer /usr/local/bin/composer
 
 RUN /usr/local/bin/composer global require magento/magento-coding-standard:*
 RUN ~/.composer/vendor/bin/phpcs --config-set installed_paths ../../magento/magento-coding-standard/