Fixed a typo

in RowMatrix.scala

Author: DB Tsai <dbtsai@dbtsai.com>

Closes #959 from dbtsai/dbtsai-typo and squashes the following commits:

fab0e0e [DB Tsai] Fixed typo

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/RowMatrix.scala

@@ -416,7 +416,7 @@ class RowMatrix(
     mat
   }
 
-  /** Updates or verfires the number of rows. */
+  /** Updates or verifies the number of rows. */
   private def updateNumRows(m: Long) {
     if (nRows <= 0) {
       nRows == m