Symphony EventDispatcher update to v5

[IcaVestica]

@ikwattro
According to https://github.com/symfony/event-dispatcher/blob/master/CHANGELOG.md

Only this is changed actually

• The Event class has been removed in favor of Symfony\Contracts\EventDispatcher\Event.
• The signature of the EventDispatcherInterface::dispatch() method has been changed to dispatch($event, string $eventName = null): object.

And composer.json to pull new event dispatcher

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[graphaware-bot]

Dear @IcaVestica,

thank you very much for your Github contributions to GraphAware's
software. In order for us to be able to accept and keep your
contributions, we would like to ask you to download, fill in, sign, and send us
a photo / scanned copy of the attached Contributor License Agreement to cla@graphaware.com .

Thank you very much in advance,

Kind Regards,

The GraphAware Team