Update dependency postcss to v8.4.21

Author: renovate[bot]

package.json

@@ -60,7 +60,7 @@
 		"eslint-config-recommended": "4.1.0",
 		"eslint-plugin-compat": "4.0.2",
 		"mini-css-extract-plugin": "2.7.2",
-		"postcss": "8.4.20",
+		"postcss": "8.4.21",
 		"postcss-calc": "8.2.4",
 		"postcss-cli": "10.1.0",
 		"postcss-color-mod-function": "3.0.3",

yarn.lock

@@ -7593,10 +7593,10 @@ postcss-watch-folder@2.0.0:
   resolved "https://registry.yarnpkg.com/postcss-watch-folder/-/postcss-watch-folder-2.0.0.tgz#0f0b22da8add6cc626be2fd86d099cc7c970b75f"
   integrity sha512-afXH6ow2TFIyCKmQiTjCbjzLOpc1cN4Tsr5J5hctLyQYfIo05pVIiADoKWOaHU8k3Axx/smL6x99Y4dDQyx7fA==
 
-postcss@8.4.20, postcss@^8.4.20:
-  version "8.4.20"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.20.tgz#64c52f509644cecad8567e949f4081d98349dc56"
-  integrity sha512-6Q04AXR1212bXr5fh03u8aAwbLxAQNGQ/Q1LNa0VfOI06ZAlhPHtQvE4OIdpj4kLThXilalPnmDSOD65DcHt+g==
+postcss@8.4.21:
+  version "8.4.21"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.21.tgz#c639b719a57efc3187b13a1d765675485f4134f4"
+  integrity sha512-tP7u/Sn/dVxK2NnruI4H9BG+x+Wxz6oeZ1cJ8P6G/PZY0IKk4k/63TDsQf2kQq3+qoJeLm2kIBUNlZe3zgb4Zg==
   dependencies:
     nanoid "^3.3.4"
     picocolors "^1.0.0"
@@ -7647,6 +7647,15 @@ postcss@^8.4.19:
     picocolors "^1.0.0"
     source-map-js "^1.0.2"
 
+postcss@^8.4.20:
+  version "8.4.20"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.20.tgz#64c52f509644cecad8567e949f4081d98349dc56"
+  integrity sha512-6Q04AXR1212bXr5fh03u8aAwbLxAQNGQ/Q1LNa0VfOI06ZAlhPHtQvE4OIdpj4kLThXilalPnmDSOD65DcHt+g==
+  dependencies:
+    nanoid "^3.3.4"
+    picocolors "^1.0.0"
+    source-map-js "^1.0.2"
+
 prebuild-install@^7.1.1:
   version "7.1.1"
   resolved "https://registry.yarnpkg.com/prebuild-install/-/prebuild-install-7.1.1.tgz#de97d5b34a70a0c81334fd24641f2a1702352e45"