[MLlib] fix typo

fix typo: it should be "default:" instead of "default;"

Author: Jacky Li <jackylk@users.noreply.github.com>

Closes #4713 from jackylk/patch-10 and squashes the following commits:

15daf2e [Jacky Li] [MLlib] fix typo

examples/src/main/scala/org/apache/spark/examples/mllib/DenseKMeans.scala

@@ -56,7 +56,7 @@ object DenseKMeans {
         .text(s"number of clusters, required")
         .action((x, c) => c.copy(k = x))
       opt[Int]("numIterations")
-        .text(s"number of iterations, default; ${defaultParams.numIterations}")
+        .text(s"number of iterations, default: ${defaultParams.numIterations}")
         .action((x, c) => c.copy(numIterations = x))
       opt[String]("initMode")
         .text(s"initialization mode (${InitializationMode.values.mkString(",")}), " +