v1.1.0. Use node cluster load balancer.

This is a fix for an issue when mixdown cluster
works behind nginx reversed proxy.
Master process accepted connection and sent it
to workers process. Pipelined http requests were
lost en route.

Browsers did fallback from pipelined mode to
keep-alive only so no issue with browser directly
connecting to mixdown.

This implementation uses cluster built-in socket 
sharing and load balancing.