Add net60 and netcoreapp3.1 targets

[jon-armen]

See #2410
Fixes #2418

[CLAassistant]

All committers have signed the CLA.

[k3davis]

I hope this can be merged soon! Appears to be just a missing framework install on your CI platform...?

[jon-armen]

I hope this can be merged soon! Appears to be just a missing framework install on your CI platform...?

I didn't have a chance to follow up on the CI side, I had just gotten the code running locally. Thanks for pointing out, I'll see if the repo has the related files that would need to be updated to get that part working.

[jon-armen]

@jchen293 , what would the timeline be for this being merged in?

[k3davis]

Pretty please merge this... :)

[jon-armen]

@remi-stripe , @richardm-stripe , what would be the timeline for this to be merged?

[richardm-stripe]

Hello, thank you for the contribution @jon-armen. Very sorry for the delay on this, it has been released in v39.90.0.