fix typescript, test node 12 and package updates

[chrisblossom]

No description provided.

[chrisblossom]

Waiting on appveyor/ci#2921

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@9e23e7b). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #136   +/-   ##
=========================================
  Coverage          ?   98.71%           
=========================================
  Files             ?        1           
  Lines             ?       78           
  Branches          ?       27           
=========================================
  Hits              ?       77           
  Misses            ?        1           
  Partials          ?        0

Impacted Files	Coverage Δ
src/clean-webpack-plugin.ts	98.71% <100%> (ø)

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