fix: package.json & yarn.lock to reduce vulnerabilities (#370)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-POSTCSS-1255640

package.json

@@ -154,7 +154,7 @@
 		"lodash.kebabcase": "^4.1.1",
 		"lodash.lowercase": "^4.3.0",
 		"lodash.startcase": "^4.4.0",
-		"postcss": "^6.0.22",
+		"postcss": "^8.2.13",
 		"sass.js": "~0.11.1",
 		"scssphp": "https://github.com/scssphp/scssphp#v1.10.0",
 		"smartmenus": "^1.1.0",

yarn.lock

@@ -3685,6 +3685,11 @@ color@^0.11.0:
   version "1.1.0"
   resolved "git+https://github.com/Automattic/Color.js.git#29304573e7bb07c5a2d0d1898e1113f3dc13de78"
 
+colorette@^1.2.2:
+  version "1.2.2"
+  resolved "https://registry.yarnpkg.com/colorette/-/colorette-1.2.2.tgz#cbcc79d5e99caea2dbf10eb3a26fd8b3e6acfa94"
+  integrity sha512-MKGMzyfeuutC/ZJ1cba9NqcNpfeqMUcYmyF1ZFY6/Cn7CNSAKx6a+s48sqLqyAiZuaP2TcqMhoo+dlwFnVxT9w==
+
 colormin@^1.0.5:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/colormin/-/colormin-1.1.2.tgz#ea2f7420a72b96881a38aae59ec124a6f7298133"
@@ -9418,6 +9423,11 @@ nan@^2.10.0, nan@^2.9.2:
   resolved "https://registry.yarnpkg.com/nan/-/nan-2.10.0.tgz#96d0cd610ebd58d4b4de9cc0c6828cda99c7548f"
   integrity sha512-bAdJv7fBLhWC+/Bls0Oza+mvTaNQtP+1RyhhhvD95pgUJz6XM5IzgmxOkItJ9tkoCiplvAnXI1tNmmUD/eScyA==
 
+nanoid@^3.1.22:
+  version "3.1.22"
+  resolved "https://registry.yarnpkg.com/nanoid/-/nanoid-3.1.22.tgz#b35f8fb7d151990a8aebd5aa5015c03cf726f844"
+  integrity sha512-/2ZUaJX2ANuLtTvqTlgqBQNJoQO398KyJgZloL0PZkC0dpysjncRUPsFe3DUPzz/y3h+u7C46np8RMuvF3jsSQ==
+
 nanomatch@^1.2.9:
   version "1.2.13"
   resolved "https://registry.yarnpkg.com/nanomatch/-/nanomatch-1.2.13.tgz#b87a8aa4fc0de8fe6be88895b38983ff265bd119"
@@ -10752,7 +10762,7 @@ postcss@^5.0.10, postcss@^5.0.11, postcss@^5.0.12, postcss@^5.0.13, postcss@^5.0
     source-map "^0.5.6"
     supports-color "^3.2.3"
 
-postcss@^6.0.0, postcss@^6.0.1, postcss@^6.0.22, postcss@^6.0.23:
+postcss@^6.0.0, postcss@^6.0.1, postcss@^6.0.23:
   version "6.0.23"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-6.0.23.tgz#61c82cc328ac60e677645f979054eb98bc0e3324"
   integrity sha512-soOk1h6J3VMTZtVeVpv15/Hpdl2cBLX3CAw4TAbkpTJiNPk9YP/zWcD1ND+xEtvyuuvKzbxliTOIyvkSeSJ6ag==
@@ -10761,6 +10771,15 @@ postcss@^6.0.0, postcss@^6.0.1, postcss@^6.0.22, postcss@^6.0.23:
     source-map "^0.6.1"
     supports-color "^5.4.0"
 
+postcss@^8.2.13:
+  version "8.2.13"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.2.13.tgz#dbe043e26e3c068e45113b1ed6375d2d37e2129f"
+  integrity sha512-FCE5xLH+hjbzRdpbRb1IMCvPv9yZx2QnDarBEYSN0N0HYk+TcXsEhwdFcFb+SRWOKzKGErhIEbBK2ogyLdTtfQ==
+  dependencies:
+    colorette "^1.2.2"
+    nanoid "^3.1.22"
+    source-map "^0.6.1"
+
 prelude-ls@~1.1.2:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/prelude-ls/-/prelude-ls-1.1.2.tgz#21932a549f5e52ffd9a827f570e04be62a97da54"