chore(deps-dev): bump postcss from 8.4.23 to 8.4.31 (#155)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.23 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.23...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

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package.json

@@ -48,7 +48,7 @@
     "@tailwindcss/typography": "^0.4.1",
     "autoprefixer": "^10.2.6",
     "gatsby-plugin-postcss": "^4.7.0",
-    "postcss": "^8.3.0",
+    "postcss": "^8.4.31",
     "prettier": "2.3.1",
     "tailwindcss": "^2.2.4"
   }

yarn.lock

@@ -10083,10 +10083,10 @@ postcss@^7.0.27:
     picocolors "^0.2.1"
     source-map "^0.6.1"
 
-postcss@^8.1.6, postcss@^8.2.15, postcss@^8.2.9, postcss@^8.3.0, postcss@^8.3.5:
-  version "8.4.23"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.23.tgz#df0aee9ac7c5e53e1075c24a3613496f9e6552ab"
-  integrity sha512-bQ3qMcpF6A/YjR55xtoTr0jGOlnPOKAIMdOWiv0EIT6HVPEaJiJB4NLljSbiHoC2RX7DN5Uvjtpbg1NPdwv1oA==
+postcss@^8.1.6, postcss@^8.2.15, postcss@^8.2.9, postcss@^8.3.5, postcss@^8.4.31:
+  version "8.4.31"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.31.tgz#92b451050a9f914da6755af352bdc0192508656d"
+  integrity sha512-PS08Iboia9mts/2ygV3eLpY5ghnUcfLV/EXTOW1E2qYxJKGGBUtNjN76FYHnMs36RmARn41bC0AZmn+rR0OVpQ==
   dependencies:
     nanoid "^3.3.6"
     picocolors "^1.0.0"