Bump pillow from 3.4.1 to 6.2.0 in /solutionbox/ml_workbench/xgboost (#730)
Bump pillow from 3.4.1 to 6.2.0 in /solutionbox/ml_workbench/xgboost (#730)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 3.4.1 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](https://github.com/python-pillow/Pillow/compare/3.4.1...6.2.0)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
Co-authored-by: Christopher Wilcox <1a61e7a0041d068722f1c352424109b22f854ce0@google.com>
googledatalab/pydatalab,googledatalab/pydatalab,googledatalab/pydatalab