You are using the wrong definition. Here is what you need;
resolvers += Resolver.url("sbt-plugin-snapshots", new URL("http://scalasbt.artifactoryonline.com/scalasbt/sbt-plugin-snapshots/"))(Resolver.ivyStylePatterns)
addSbtPlugin("org.lifty" % "lifty" % "1.7.4")
If you want to make this available for all projects, then put in ~/.sbt/plugins/plugins.sbt
. Otherwise it goes in: ProjectFolder/project/plugins.sbt
But they don't have a Scala 2.10 or SBT 0.12 release out.. Look HERE for what is available.