Add bors.toml

[hgrecco]

• [ ] Closes # (insert issue number)
• [ ] Executed pre-commit run --all-files with no errors
• [ ] The change is fully covered by automated unit tests
• [ ] Documented in docs/ as appropriate
• [ ] Added an entry to the CHANGES file

[hgrecco]

bors r+

[bors[bot]]

Timed out.

[hgrecco]

bors r+

[bors[bot]]

Build succeeded:

• lint
• test (3.7, numpy>=1.14,<2.0.0, pandas==1.2)