[Docs] fix minor MLlib case typo

Also make the list of features consistent in style.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2278 from nchammas/patch-1 and squashes the following commits:

56df319 [Nicholas Chammas] [Docs] fix minor MLlib case typo

(cherry picked from commit 6a37ed838b3cbf96f7a904f3d3dabf99141729f5)
Signed-off-by: Xiangrui Meng <meng@databricks.com>