Update genjavadoc to 0.13

Author: srowen

project/SparkBuild.scala

@@ -219,7 +219,7 @@ object SparkBuild extends PomBuild {
       .map(file),
     incOptions := incOptions.value.withNameHashing(true),
     publishMavenStyle := true,
-    unidocGenjavadocVersion := "0.11",
+    unidocGenjavadocVersion := "0.13",
 
     // Override SBT's default resolvers:
     resolvers := Seq(