chore(deps): update dependency postcss to ^8.1.6 (#27903)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

packages/gatsby-plugin-image/package.json

@@ -63,7 +63,7 @@
     "do-sync": "^2.2.0",
     "microbundle": "^0.12.4",
     "npm-run-all": "^4.1.5",
-    "postcss": "^8.1.4",
+    "postcss": "^8.1.6",
     "terser": "^5.3.8",
     "typescript": "^3.9.5"
   },

yarn.lock

@@ -16906,10 +16906,10 @@ nan@^2.10.0, nan@^2.9.2:
   resolved "https://registry.yarnpkg.com/nan/-/nan-2.14.0.tgz#7818f722027b2459a86f0295d434d1fc2336c52c"
   integrity sha512-INOFj37C7k3AfaNTtX8RhsTw7qRy7eLET14cROi9+5HAVbbHuIWUHEauBv5qT4Av2tWasiTY1Jw6puUNqRJXQg==
 
-nanoid@^3.1.15:
-  version "3.1.15"
-  resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.1.15.tgz#28e7c4ce56aff2d0c2d37814c7aef9d6c5b3e6f3"
-  integrity sha512-n8rXUZ8UU3lV6+43atPrSizqzh25n1/f00Wx1sCiE7R1sSHytZLTTiQl8DjC4IDLOnEZDlgJhy0yO4VsIpMxow==
+nanoid@^3.1.16:
+  version "3.1.16"
+  resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.1.16.tgz#b21f0a7d031196faf75314d7c65d36352beeef64"
+  integrity sha512-+AK8MN0WHji40lj8AEuwLOvLSbWYApQpre/aFJZD71r43wVRLrOYS4FmJOPQYon1TqB462RzrrxlfA74XRES8w==
 
 nanomatch@^1.2.9:
   version "1.2.13"
@@ -19108,14 +19108,14 @@ postcss@^7.0.0, postcss@^7.0.1, postcss@^7.0.14, postcss@^7.0.17, postcss@^7.0.1
     source-map "^0.6.1"
     supports-color "^6.1.0"
 
-postcss@^8.1.4:
-  version "8.1.4"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.1.4.tgz#356dfef367a70f3d04347f74560c85846e20e4c1"
-  integrity sha512-LfqcwgMq9LOd8pX7K2+r2HPitlIGC5p6PoZhVELlqhh2YGDVcXKpkCseqan73Hrdik6nBd2OvoDPUaP/oMj9hQ==
+postcss@^8.1.6:
+  version "8.1.6"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.1.6.tgz#b022ba2cfb8701da234d073ed3128c5a384c35ff"
+  integrity sha512-JuifSl4h8dJ70SiMXKjzCxhalE6p2TnMHuq9G8ftyXj2jg6SXzqCsEuxMj9RkmJoO5D+Z9YrWunNkxqpRT02qg==
   dependencies:
     colorette "^1.2.1"
     line-column "^1.0.2"
-    nanoid "^3.1.15"
+    nanoid "^3.1.16"
     source-map "^0.6.1"
 
 potrace@^2.1.8: