Made Python 3.7 (async keyword) unsupported and bumped version to 0.5.4
Made Python 3.7 (async keyword) unsupported and bumped version to 0.5.4

nwautomator/ncclient,ncclient/ncclient,leopoul/ncclient,earies/ncclient,vnitinv/ncclient,einarnn/ncclient