HELP! Piwik won't upgrade from 3.0* to 3.2.0

After following all the steps for carrying out a manual upgrade, The index page of Piwik website displays the following error:

Fatal error: Declaration of DI\Definition\StringDefinition::resolve(Interop\Container\ContainerInterface $container) must be compatible with DI\Definition\SelfResolvingDefinition::resolve(Psr\Container\ContainerInterface $container) in /home/public/vendor/php-di/php-di/src/DI/Definition/StringDefinition.php on line 16

Some have suggested that this is due to the limitation of using MariaDB version 5.3 instead of 10 as the SQL database. PHP is the latest version.

But there should be a better diagnosis.Website permissions are OK.

Please note that I use a shared hosting environment, not su_php.