Hummingbird v0.2.2

This release includes several bug fixes, version upgrades, and minor feature upgrades.

Versioning changes:

• Upgrading to Torch 1.8.0
• Deprecating Python 3.5

Notable bug fixes:

• Fix save to pytorch for onnx models with trees (#425)
• Fix bug with degenerate trees (#426)
• Fix bloated models when saving (#429)

Also included are fixes to test flakiness and error messages.

Feature upgrades:

• Add support for modified huber loss in SGD (#415)
• Simplify the discretizer logic (#448)

Credits:

Thanks to our first-time contributors qin-xiong and sleepy-owl