(DOCUMENT-107) This commit fixes a typo in the Database Optmization section of the PE Documentation.

This fixes a typo in the docs for versions 3.0 - 3.2 of the PE docs where the word "model" was used instead of the word "mode"
Merge pull request #332 from llowder/fix_for_DOCUMENT-107

(DOCUMENT-107) This commit fixes a typo in the Database Optimization sect...