Python 3.7 support

[johnthagen]

The script still works as of Python 3.6, but I believe it will break in Python 3.7. This is the output of flake8:

pypy_setup.py:1070:18: W606 'async' and 'await' are reserved keywords starting with Python 3.7

[BraINstinct0]

pypy is currently not compatible with python 3.7, so this cannot be solved unless the team behind pypy makes a new release.

[johnthagen]

@BraINstinct0 Specifically, I was thinking that if Python 3.7 keywords are being used these identifiers could be renamed now to prepare for Python 3.7 support in PyPy.

I agree that today this isn't an immediate problem because there is no PyPy 3.7 yet.

[wh1t3h47]

See unbit/uwsgi#2342 for reference on how to fix

However, I don't know if .property and ['property'] are 100% compatible, I think trying to reference a key that doesn't exist with [] will error out, so may be helpful to check if async exists inside the object as well