Update architecture_design.md
Update architecture_design.md

Remove an extra space in a link.  This wasn't showing up as a link on readthedocs
uber-node/ringpop-node,esatterwhite/skyring,uber/ringpop-node,hj3938/ringpop,sasa233/ringpop,Collin-V/ringpop,uber/ringpop,tomasdiez/ringpop,uber/ringpop-node,esatterwhite/skyring,hotrannam/ringpop,uber-node/ringpop-node