Finished a TODO for comments in Strategy.scala

mllib/src/main/scala/org/apache/spark/mllib/tree/configuration/Strategy.scala

@@ -55,7 +55,8 @@ import org.apache.spark.mllib.tree.impurity.{Entropy, Gini, Impurity, Variance}
  * @param minInfoGain Minimum information gain a split must get. Default value is 0.0.
  *                    If a split has less information gain than minInfoGain,
  *                    this split will not be considered as a valid split.
- * @param pruneTree <TODO>
+ * @param pruneTree If this is true, the final training tree will undergo a pruning in which
+ *                  nodes with the same classifications are merged.
  * @param maxMemoryInMB Maximum memory in MB allocated to histogram aggregation. Default value is
  *                      256 MB.  If too small, then 1 node will be split per iteration, and
  *                      its aggregates may exceed this size.