Cannot run with python 3.7

[JiseongKim]

async is a reserved word in Python 3.7

So, I think change install instruction like the following

conda create -n elf python=3.6 (or 3.x)

or change parameter name('async') to the other.

[douglasrizzo]

I think this and #124 are related. I just sent #135 to fix this.