Bump clean-css from 3.4.5 to 4.1.11

Bumps [clean-css](https://github.com/jakubpawlowicz/clean-css) from 3.4.5 to 4.1.11.
- [Release notes](https://github.com/jakubpawlowicz/clean-css/releases)
- [Changelog](https://github.com/jakubpawlowicz/clean-css/blob/master/History.md)
- [Commits](clean-css/clean-css@v3.4.5...v4.1.11)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -20,7 +20,7 @@
     "browser-sync": "^2.26.7",
     "browserify": "10.1.0",
     "buffer-crc32": "~0.2.1",
-    "clean-css": "^3.3.1",
+    "clean-css": "^4.1.11",
     "colors": "^1.0.3",
     "commander": "^2.7.1",
     "debug": "^2.1.3",