chore(deps): update dependency postcss to v8 [skip netlify] (#2833)

* chore(deps): update dependency postcss to v8 [skip netlify]

* chore: update css-loader, cssnano, postcss-loader

Co-authored-by: Renovate Bot <bot@renovateapp.com>
Co-authored-by: Young Min Kin <mail@ylem.kim>

package.json

@@ -36,8 +36,8 @@
     "browserslist": "^4.13.0",
     "browserstack-local": "^1.4.5",
     "caniuse-lite": "^1.0.30001102",
-    "css-loader": "^4.0.0",
-    "cssnano": "^4.1.10",
+    "css-loader": "^5.1.2",
+    "cssnano": "^5.0.0-rc.1",
     "eslint": "^7.4.0",
     "eslint-plugin-actions": "^1.0.1",
     "eslint-plugin-flowtype": "^5.2.0",
@@ -63,8 +63,8 @@
     "mini-css-extract-plugin": "^1.0.0",
     "mkdirp": "^1.0.4",
     "pako": "^2.0.0",
-    "postcss": "^7.0.32",
-    "postcss-loader": "^4.0.0",
+    "postcss": "^8.0.0",
+    "postcss-loader": "^5.2.0",
     "postcss-preset-env": "^6.7.0",
     "prettier": "^2.0.5",
     "query-string": "^6.2.0",