Typehint parameters in accordance with ContainerInterface

[dnwjn]

Hi team!

We ran into an issue with the Restrict Content plugin and the WP CLI. We would get the following exception:

PHP Fatal error:  Declaration of Illuminate\Container\Container::get(string $id) must be compatible with Psr\Container\ContainerInterface::get($id) in /<redacted>/vendor/illuminate/container/Container.php on line 714

We pinpointed the issue to be in your plugin as disabling it, or typehinting the parameters as done in this PR, would resolve it.