Bump pillow from 4.2.1 to 6.2.0 in /example (#217)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 4.2.1 to 6.2.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@4.2.1...6.2.0)

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