refactor: use async/await where applicable

[raphinesse]

Motivation and Context

Preparation of a potential fix for apache/cordova-lib#859

Also: apache/cordova#175

Description

Use async/await where applicable

Testing

All automated tests still pass

[codecov-io]

Codecov Report

Merging #89 into master will increase coverage by 0.11%.
The diff coverage is 89.74%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   92.30%   92.42%   +0.11%     
==========================================
  Files           1        1              
  Lines          65       66       +1     
==========================================
+ Hits           60       61       +1     
  Misses          5        5              

Impacted Files	Coverage Δ
index.js	92.42% <89.74%> (+0.11%)	⬆️

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[dpogue]

One of these days I suppose I'll get used to this newfangled syntax, but I still think promises are more readable and make the async steps more explicit 😛

[raphinesse]

One of these days I suppose I'll get used to this newfangled syntax, but I still think promises are more readable and make the async steps more explicit

Promises are definitely more explicit and allow for very pretty code sometimes. And I also agree with async/await taking some getting used to. But once you are used to it, I think it really excels at making control flow involving async functions easier and more readable.

Anyway, thanks for the reviews 🙇