Bumped smmap upper bound

[tmcclintock]

Closes #67

Tests passed locally.

[Byron]

Thanks a bunch!

Could you also increase the gitdb version number to something you find suitable for such a change?
My problem is that I don't really know what's going on and why things are breaking down as they do, originally @Harmon758 did tremendous work to assure of that.

[Harmon758]

@Byron A patch version bump should be fine for this.

[Byron]

Thanks, @Harmon758 , I just published v4.0.6, unfortunately along with 4.0.5 as that one was apparently still lying around locally. It's interesting to see how pypi allows overwriting/altering already published versions. Let's hope that doesn't break things.

View at:
https://pypi.org/project/gitdb/4.0.6/
https://pypi.org/project/gitdb/4.0.5/

[Harmon758]

v4.0.5 was already released on May 4, 2020, and you can't alter or overwrite existing releases, so I don't think anything happened with that version.