[SPARK-16485][DOC][ML] Fixed several inline formatting in ml features doc
[SPARK-16485][DOC][ML] Fixed several inline formatting in ml features doc

## What changes were proposed in this pull request?

Fixed several inline formatting in ml features doc.

Before:

<img width="475" alt="screen shot 2016-07-14 at 12 24 57 pm" src="https://cloud.githubusercontent.com/assets/717363/16827974/1e1b6e04-49be-11e6-8aa9-4a0cb6cd3b4e.png">

After:

<img width="404" alt="screen shot 2016-07-14 at 12 25 48 pm" src="https://cloud.githubusercontent.com/assets/717363/16827976/2576510a-49be-11e6-96dd-92a1fa464d36.png">

## How was this patch tested?

Genetate the docs locally by `SKIP_API=1 jekyll build` and view it in the browser.

Author: Shuai Lin <linshuai2012@gmail.com>

Closes #14194 from lins05/fix-docs-formatting.

(cherry picked from commit 3b6e1d094e153599e158331b10d33d74a667be5a)
Signed-off-by: Sean Owen <291c18f3fb7528c712d9098b0e50a515ea0b91d5@cloudera.com>

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