fix typo preventing event handler firing
fix typo preventing event handler firing

`options.OnEvent` is documented as `options.onEvent`. Assuming consistency with other events, and `_options.onEvent` was intended, fixing typo here instead of in [docs](https://github.com/jbillmann/GarageServer.IO/blob/master/documentation/ServerAPI.md#server-options).
jbillmann/GarageServer.IO,maritz/GarageServer.IO,maritz/GarageServer.IO,jbillmann/GarageServer.IO