use versioned wp-cli

Dockerfile

@@ -12,7 +12,7 @@ ADD start.sh /app/code/start.sh
 RUN mkdir -p /run/wordpress/sessions && \
     ln -sf /run/wordpress/wp-config.php /app/code/wp-config.php
 
-RUN curl -o /app/code/wp https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
+RUN curl -L -o /app/code/wp https://github.com/wp-cli/wp-cli/releases/download/v0.23.0/wp-cli-0.23.0.phar
 RUN chmod +x /app/code/wp
 # https://github.com/wp-cli/wp-cli/issues/1164
 RUN echo "<?php function wp_new_blog_notification() {} ?>" > /run/wordpress/disable-new-blog-notification.php