Update Cython version

[tigert1998]

No description provided.

[AndriyMulyar]

Would like to test this myself before merging. Will not get to it for a bit though.

[tigert1998]

I am using python3.9 from anaconda. I found that I cannot use this repo. After I updated Cython everything went fine. I think more people would use the new version from now on so using the new Cython is urgent.

[ZiruiYan]

This works for me with python3.9! And when I install in mac, I need to change "malloc.h" to "stdlib.h" and meet lots of "non-void function 'XXX' should return a value" error for the original C code.

But always Restarting kernel... when run the example code...

[tigert1998]

This works for me with python3.9! And when I install in mac, I need to change "malloc.h" to "stdlib.h" and meet lots of "non-void function 'XXX' should return a value" error for the original C code.

But always Restarting kernel... when run the example code...

I took a look at your forked repo. It seems that the original C code does not work well with clang because it uses the behaviour that return means return null.