Python 3.7+ broken, is this library actively maintianed?

Hi,

Running on Python >= 3.7 is broken due to changes introduced in Python 3.7 around reserving 'async' keyword. https://docs.python.org/3.7/whatsnew/3.7.html#summary-release-highlights

Is this library still maintained?

Thanks!

```
killbill\api\account_api.py", line 179
    async=params.get('async'),
    ^^^^^
SyntaxError: invalid syntax
```