Updated comment reference to 1.3.6 in DBUtil

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | -
| Refs tickets  | -
| License       | MIT
| Doc PR        | -

Trivial update, where this comment should be 1.3.7, where categories_mapobj is nog there any more.
Merge pull request #1602 from espaan/patch-29

Updated comment reference to 1.3.6 in DBUtil