[MINOR][DOCS] Added Missing back slashes
[MINOR][DOCS] Added Missing back slashes

## What changes were proposed in this pull request?

When studying spark many users just copy examples on the documentation and paste on their terminals
and because of that the missing backlashes lead them run into some shell errors.

The added backslashes avoid that problem for spark users with that behavior.

## How was this patch tested?

I generated the documentation locally using jekyll and checked the generated pages

Author: Daniel Santana <mestresan@gmail.com>

Closes #11699 from danielsan/master.

(cherry picked from commit 9f13f0fc1724e407d3be54152b82150a16395421)
Signed-off-by: Andrew Or <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@databricks.com>

haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark