Update event-bus.rst

**Previous version:**
    A plugin could subscribe to the BlockChangeEvent and still receive BlockBreakEvent events.
    However, a plugin subscribed to just BlockChangeEvent would not receive other types of BlockBreakEvent.

If ``BlockBreakEvent`` extends ``BlockChangeEvent``, the 2nd sentence should say the opposite.

**Fixed version:**
However, a plugin subscribed to just BlockBreakEvent would not receive other types of BlockChangeEvent