v4.0.0

Minimal change in this upgrade but since the monitor$ notification event now signals with the error object rather than the error.message, I thought it was best to bump the major version so it wouldn't surprise anyone.

monitor$ event example error

{ action: { type: 'BAD' },
          err: Error('something bad happened'), // this is now an error object if one was thrown rather than a string
          op: 'nextError' },

Unless you are using monitor$ and specifically looking for a string, you can safely upgrade to this version. Even if you were using the result as a string error should automatically coerce into a string as well.