`"connection"` event on `Ros` class renamed to `"open"`

[EzraBrooks]

@dsobek found an issue: an unexpected(?) rename of the connection event on the Ros class. fixing.

Originally posted by @EzraBrooks in #1089

@douglascayers I'm not sure if this was accidental or a deliberate rename for consistency. If deliberate, I think we should probably do it with a deprecation notice for 3.0 - to align with my desire to not break the default constructor functionality for Ros in this version.

[douglascayers]

It was deliberate and thought it'd be ok since 2.0 was making some breaking changes. I'm good to keep it as "connection" too and/or proposal to phase it to "open" via deprecation

Thanks

[EzraBrooks]

No worries, it's my bad for not catching it during review!

If you'd like to reimplement the change with some sort of detection for users still adding an event handler on connection I'd be very amenable to that. I just think this is a pretty big API to break since it's introduced as early as the README to users