Updated link to SBT

docs/index.md

@@ -18,7 +18,7 @@ or you will need to set the `SCALA_HOME` environment variable to point
 to where you've installed Scala. Scala must also be accessible through one
 of these methods on slave nodes on your cluster.
 
-Spark uses [Simple Build Tool](https://github.com/harrah/xsbt/wiki), which is bundled with it. To compile the code, go into the top-level Spark directory and run
+Spark uses [Simple Build Tool](http://www.scala-sbt.org), which is bundled with it. To compile the code, go into the top-level Spark directory and run
 
     sbt/sbt package