Fix typos: thubm -> thumb(nail)

[grayeul]

Description & Issue number it closes

This just creates an annoying typo [thubm => thumb(nail) ]

Screenshots (if appropriate)

N/A

How to test the changes?

N/A

Type of change

• Bug fix (non-breaking change which fixes an issue) (cosmetic variable name typo)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Just added a new person and verified a thumbnail image can be created and displayed.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules