support for python 3.7

[tomplus]

Python 3.7 treats async as a reserved keyword.
Client is updated by fixed swagger-codegen (swagger-api/swagger-codegen#8401).

[codecov-io]

Codecov Report

Merging #28 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #28   +/-   ##
=======================================
  Coverage   93.48%   93.48%           
=======================================
  Files          16       16           
  Lines         967      967           
=======================================
  Hits          904      904           
  Misses         63       63

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 29b955a...61a7fdd. Read the comment docs.