Update gevent to the last major version

[AlexBenny]

Gevent dependency recently released a new major version.
we plan to update it in the next Python tracker release which is currently scheduled for Q4 2020.

[camerondavison]

I am getting

<frozen importlib._bootstrap>:219: RuntimeWarning: greenlet.greenlet size changed, may indicate binary incompatibility. Expected 144 from C header, got 152 from PyObject

which i think is caused by not being on the latest version of gevent python-greenlet/greenlet#178 would it be worth locking down greenlet to a version <= 0.4.16 until gevent is updated to 20.9.0 python-greenlet/greenlet#178 (comment) ?

[paulboocock]

Thanks for pointing this out @camerondavison. Looks like this is in a bit of a tangle, I'll look to get this sorted out soon.

[paulboocock]

Hi @camerondavison we've just published 0.8.4 to lock greenlet to a version <= 0.4.16 until we get to bumping gevent in 0.9.0.