chore(deps): update dependency imagemin-gifsicle to v7

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
imagemin-gifsicle	dependencies	major	^6.0.1 -> ^7.0.0

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Release Notes

imagemin/imagemin-gifsicle

### [`v7.0.0`](https://togithub.com/imagemin/imagemin-gifsicle/releases/v7.0.0) [Compare Source](https://togithub.com/imagemin/imagemin-gifsicle/compare/v6.0.1...v7.0.0) ##### Breaking - Require Node.js 10 [`a5feafd`](https://togithub.com/imagemin/imagemin-gifsicle/commit/a5feafd) ##### Enhancements - Update `gifsicle` dependency [`68b9a4d`](https://togithub.com/imagemin/imagemin-gifsicle/commit/68b9a4d) - Optimize images in memory [`ac13852`](https://togithub.com/imagemin/imagemin-gifsicle/commit/ac13852)

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