Update dependency sass-loader to v8

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
sass-loader	devDependencies	major	7.3.1 -> 8.0.0

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Release Notes

webpack-contrib/sass-loader

v8.0.0

Compare Source

⚠ BREAKING CHANGES

• minimum required webpack version is 4.36.0
• minimum required node.js version is 8.9.0
• move all sass (includePaths, importer, functions) options to the sassOptions option. The functions option can't be used as Function, you should use sassOption as Function to achieve this.
• the data option was renamed to the prependData option
• default value of the sourceMap option depends on the devtool value (eval/false values don't enable source map generation)

Features

• automatically use the fibers package if it is possible (#​744) (96184e1)
• source map generation depends on the devtool option (#​743) (fcea88e)
• validate loader options (#​737) (7b543fc)
• reworked error handling from node-sass/sass
• improve resolution for @import (including support _index and index files in a directory)

Bug Fixes

• compatibility with pnp

7.3.1 (2019-08-20)

Bug Fixes

• minimum node version in package.json (#​733) (1175920)

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[coveralls]

Pull Request Test Coverage Report for Build 235

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.906%

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Totals
Change from base Build 233:	0.0%
Covered Lines:	45
Relevant Lines:	53

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💛 - Coveralls