Invalid method implementation in README

[qsdigor]

I have found that the readme is not up to date.
The section about https://github.com/ably/ably-java#channel-state is using an old method that does not exist anymore.

Old method

@Override
public void onChannelStateChanged(ChannelState state, ErrorInfo reason) {
    System.out.println("Channel state changed to " + state.name());
    if (reason != null) System.out.println(reason.toString());
}

New method

@Override
public void onChannelStateChanged(ChannelStateChange stateChange) {

}

┆Issue is synchronized with this Jira Story by Unito