Update dependency postcss-combine-duplicated-selectors to v9

Author: renovate-bot

package.json

@@ -83,7 +83,7 @@
     "mkdirp": "1.0.4",
     "node-sass": "4.14.1",
     "postcss": "7.0.32",
-    "postcss-combine-duplicated-selectors": "8.1.0",
+    "postcss-combine-duplicated-selectors": "9.0.0",
     "postcss-custom-properties": "8.0.11",
     "postcss-remove-root": "0.0.2",
     "prettier": "2.0.5",