[Minor] Fix scala doc

Minor fix for an obvious scala doc error.

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #3751 from viirya/fix_scaladoc and squashes the following commits:

03fddaa [Liang-Chi Hsieh] Fix scala doc.
[SPARK-4920][UI]:current spark version in UI is not striking.

It is not convenient to see the Spark version. We can keep the same style with Spark website.

![spark_version](https://cloud.githubusercontent.com/assets/7402327/5527025/1c8c721c-8a35-11e4-8d6a-2734f3c6bdf8.jpg)

Author: genmao.ygm <genmao.ygm@alibaba-inc.com>

Closes #3763 from uncleGen/master-clean-141222 and squashes the following commits:

0dcb9a9 [genmao.ygm] [SPARK-4920][UI]:current spark version in UI is not striking.