Update dependency postcss-load-config to v3 (postcss#351)

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

Author: renovate[bot]

package.json

@@ -24,7 +24,7 @@
     "fs-extra": "^9.0.0",
     "get-stdin": "^8.0.0",
     "globby": "^11.0.0",
-    "postcss-load-config": "^2.1.1",
+    "postcss-load-config": "^3.0.0",
     "postcss-reporter": "^7.0.0",
     "pretty-hrtime": "^1.0.3",
     "read-cache": "^1.0.0",