[SPARK-11383][DOCS] Replaced example code in mllib-naive-bayes.md/mllib-isotonic-regression.md using include_example

I have made the required changes in mllib-naive-bayes.md/mllib-isotonic-regression.md and also verified them.
Kindle Review it.

Author: Rishabh Bhardwaj <rbnext29@gmail.com>

Closes #9353 from rishabhbhardwaj/SPARK-11383.