upgrade README instructions to recent version 0.7.1
upgrade README instructions to recent version 0.7.1

xuwei-k/xsbt,mdedetrich/sbt,sbt/sbt,xuwei-k/xsbt,sbt/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,jrudolph/sbt-dependency-graph,sbt/sbt,mdedetrich/sbt,sbt/sbt,mdedetrich/sbt,xuwei-k/xsbt,sbt/sbt,xuwei-k/xsbt,xuwei-k/xsbt,mdedetrich/sbt,mdedetrich/sbt,mdedetrich/sbt