delete unstable rethinkdb install instructions now that rethink 2.1 is out
delete unstable rethinkdb install instructions now that rethink 2.1 is out

DrXyzzy/smc,sagemathinc/smc,sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,tscholl2/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc