Bump websockify to >=0.6.0 which fixes bug causing zombie processes

Websockify 0.6.0 has been released for more than half an year, and
it fixes bug causing zombie processes on certain systems when using
multiprocessing.

Ref: https://github.com/kanaka/websockify/issues/95

Closes-Bug: #1048703

Change-Id: I5c13ee3504bd1542f936c34082d4bbdc498315ce
Merge "Bump websockify to >=0.6.0 which fixes bug causing zombie processes"