Fixed a 404 -- missing '.html'

docs/tuning.md

@@ -233,7 +233,7 @@ number of cores in your clusters.
 
 ## Broadcasting Large Variables
 
-Using the [broadcast functionality](scala-programming-guide#broadcast-variables)
+Using the [broadcast functionality](scala-programming-guide.html#broadcast-variables)
 available in `SparkContext` can greatly reduce the size of each serialized task, and the cost
 of launching a job over a cluster. If your tasks use any large object from the driver program
 inside of them (e.g. a static lookup table), consider turning it into a broadcast variable.