Update dependency postcss-value-parser to v4 (#423)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

package.json

@@ -21,7 +21,7 @@
     "node": ">=10.0.0"
   },
   "dependencies": {
-    "postcss-value-parser": "^3.2.3",
+    "postcss-value-parser": "^4.0.0",
     "read-cache": "^1.0.0",
     "resolve": "^1.1.7"
   },