Update @fullhuman/postcss-purgecss to version 4.0.3 (tailwindlabs#3913)

Co-authored-by: depfu[bot] <23717796+depfu[bot]@users.noreply.github.com>

Author: depfu[bot]

package-lock.json

@@ -64,7 +64,7 @@
     "postcss": "^8.0.9"
   },
   "dependencies": {
-    "@fullhuman/postcss-purgecss": "^3.1.3",
+    "@fullhuman/postcss-purgecss": "^4.0.3",
     "bytes": "^3.0.0",
     "chalk": "^4.1.1",
     "chokidar": "^3.5.1",