chore(deps): update dependency imagemin-pngquant to v9

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
imagemin-pngquant	dependencies	major	^8.0.0 -> ^9.0.0

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Release Notes

imagemin/imagemin-pngquant

### [`v9.0.0`](https://togithub.com/imagemin/imagemin-pngquant/releases/v9.0.0) [Compare Source](https://togithub.com/imagemin/imagemin-pngquant/compare/v8.0.0...v9.0.0) - Require Node.js 10 ([#​67](https://togithub.com/imagemin/imagemin-pngquant/issues/67)) [`d285e92`](https://togithub.com/imagemin/imagemin-pngquant/commit/d285e92)

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[codecov[bot]]

Codecov Report

Merging #15 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #15   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files            2         2           
  Lines           13        13           
  Branches         2         2           
=========================================
  Hits            13        13           

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