deps: update dependencies

package.json

@@ -11,7 +11,7 @@
   "dependencies": {
     "bootstrap-sass": "^3.4.1",
     "browser-sync": "^2.26.14",
-    "cssnano": "^4.1.10",
+    "cssnano": "^5.0.2",
     "gulp": "^4.0.2",
     "gulp-changed": "^4.0.2",
     "gulp-clean-css": "^4.3.0",
@@ -23,6 +23,7 @@
     "gulp-sass": "^4.1.0",
     "gulp-util": "^3.0.8",
     "merge-stream": "^2.0.0",
+    "postcss": "^8.2",
     "yarn": "^1.22.10"
   }
 }