Bump css-loader from 4.0.0 to 6.7.1 (#4927)

Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 4.0.0 to 6.7.1.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/css-loader/compare/v4.0.0...v6.7.1)

---
updated-dependencies:
- dependency-name: css-loader
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -19,7 +19,7 @@
     "codecov":"3.8.3",
     "copy-webpack-plugin": "11.0.0",
     "cross-env": "7.0.3",
-    "css-loader": "4.0.0",
+    "css-loader": "6.7.1",
     "d3-axis": "3.0.0",
     "d3-scale": "3.3.0",
     "d3-selection": "3.0.0",