[SPARK-1105] fix site scala version error in doc

https://spark-project.atlassian.net/browse/SPARK-1105

fix site scala version error

Author: CodingCat <zhunansjtu@gmail.com>

Closes #616 from CodingCat/doc_version and squashes the following commits:

eafd99a [CodingCat] fix site scala version error in doc

(cherry picked from commit d99773d5bba674cc1434c86435b6d9b3739314c8)
Signed-off-by: Aaron Davidson <aaron@databricks.com>

Conflicts:
	docs/_config.yml