async not work properly on windows and macOS
my test file https://github.com/bung87/scorper/blob/devel/tests/trange.nim  
always fails on windows and macOS, on my local machine macOS runs it will randomly fails, it contains three client request server tests, one of them will get empty body string.

you can check my CI tests here:  
https://github.com/bung87/scorper/actions/runs/714168854  

I also notice CI of nim-chronos on windows and macOS not actually runs.  