Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.9.0 to 1.15.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](https://github.com/tensorflow/tensorflow/compare/v1.9.0...v1.15.2

)

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

Dev

Extract the disappeared cells as well

Dev

This reverts commit 7d3d3464.

image loader

Dev

This reverts commit 8e45af01.

Dev

Making pairwise comparisons for cell merging faster.