Add memory_limit to php.ini (#5105)

frameworks/PHP/ubiquity/deploy/conf/php-async.ini

@@ -5,4 +5,6 @@ opcache.save_comments=0
 opcache.enable_file_override=1
 opcache.huge_code_pages=1
 
-mysqlnd.collect_statistics = Off
+mysqlnd.collect_statistics = Off
+
+memory_limit = 512M