dramatiq dependencies

[rpkilby]

I noticed that by default, dramatiq installs the dependencies for rabbitmq and the watch feature. I think this is due to the following lines:

dramatiq/setup.py

Lines 44 to 47 in f6cea0d

	extra_dependencies[""] = list(set(
	extra_dependencies["rabbitmq"] +
	extra_dependencies["watch"]
	))

Executing pip install dramatiq[redis] will still install in the rabbitmq and watch dependencies.