fix deprecated calls to EventEmitterTrait, use get/setEventEmitter

Fixes the following fatal error when using v. 1.1.0 of php-event-manager:
```
HTTP: Analyzing TCP request.
PHP Fatal error:  Call to a member function send() on a non-object in /var/www/sandbox/php-io/src/Gplanchat/Io/Net/Protocol/Http/Upgrade/WebSocket/RequestHandler.php on line 59
PHP Stack trace:
PHP   1. {main}() /var/www/sandbox/php-io/src/server.php:0
PHP   2. Gplanchat\Io\Application\Application->run() /var/www/sandbox/php-io/src/server.php:105
PHP   3. Gplanchat\Io\Adapter\Libuv\Loop\Loop->run() /var/www/sandbox/php-io/src/Gplanchat/Io/Application/Application.php:127
PHP   4. uv_run() /var/www/sandbox/php-io/src/Gplanchat/Io/Adapter/Libuv/Loop/Loop.php:108
PHP   5. Gplanchat\Io\Adapter\Libuv\EventManager\CallbackHandler->Gplanchat\Io\Adapter\Libuv\EventManager\{closure}() /var/www/sandbox/php-io/src/Gplanchat/Io/Adapter/Libuv/Loop/Loop.php:108
PHP   6. call_user_func_array:{/var/www/sandbox/php-io/src/Gplanchat/Io/Adapter/Libuv/EventManager/CallbackHandler.php:75}() /var/www/sandbox/php-io/src/Gplanchat/Io/Adapter/Libuv/EventManager/CallbackHandler.php:75
PHP   7. Gplanchat\Io\Net\Protocol\Http\Upgrade\WebSocket\RequestHandler->__invoke() /var/www/sandbox/php-io/src/Gplanchat/Io/Adapter/Libuv/EventManager/CallbackHandler.php:75
PHP   8. Gplanchat\Io\Net\Protocol\Http\Upgrade\WebSocket\RequestHandler->emit() /var/www/sandbox/php-io/src/Gplanchat/Io/Net/Protocol/Http/Upgrade/WebSocket/RequestHandler.php:137
PHP   9. Gplanchat\EventManager\CallbackHandler->call() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/EventEmitterTrait.php:240
PHP  10. call_user_func_array:{/var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51}() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51
PHP  11. {closure:/var/www/sandbox/php-io/src/server.php:90-95}() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51
PHP  12. Gplanchat\Io\Net\Protocol\Http\Upgrade\WebSocket\Response->emit() /var/www/sandbox/php-io/src/server.php:93
PHP  13. Gplanchat\EventManager\CallbackHandler->call() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/EventEmitterTrait.php:240
PHP  14. call_user_func_array:{/var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51}() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51
PHP  15. Gplanchat\Io\Net\Protocol\Http\Upgrade\WebSocket\RequestHandler->Gplanchat\Io\Net\Protocol\Http\Upgrade\WebSocket\{closure}() /var/www/sandbox/php-io/vendor/gplanchat/php-event-manager/src/CallbackHandler.php:51
```