Update asyncio example to use async/await syntax in Python 3.7 or later

[kamalgill]

Changes proposed in this pull request:

• Update asyncio example to use async/await syntax in Python 3.7 or later

Attention: @prkumar

[codecov]

Codecov Report

Merging #218 (b87101c) into master (3ade04d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #218   +/-   ##
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  Coverage   99.91%   99.91%           
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  Files          44       44           
  Lines        2398     2398           
  Branches      182      182           
=======================================
  Hits         2396     2396           
  Misses          2        2           

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