Update dependency node-sass to v4.12.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
node-sass	devDependencies	minor	4.11.0 -> 4.12.0	source

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Release Notes

sass/node-sass

### [`v4.12.0`](https://togithub.com/sass/node-sass/blob/master/CHANGELOG.md#v4120) [Compare Source](https://togithub.com/sass/node-sass/compare/v4.11.0...v4.12.0)

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