Move postcss to dependencies

We have a bunch of production scripts that
require "postcss" to be installed in production mode.

package.json

@@ -155,6 +155,7 @@
     "pikaday": "^1.8.0",
     "popper.js": "^1.16.1",
     "portal-vue": "^2.1.7",
+    "postcss": "8.4.5",
     "prismjs": "^1.21.0",
     "prosemirror-markdown": "1.7.1",
     "prosemirror-model": "^1.16.1",
@@ -239,7 +240,6 @@
     "miragejs": "^0.1.40",
     "mock-apollo-client": "1.2.0",
     "nodemon": "^2.0.4",
-    "postcss": "^8.4.5",
     "prettier": "2.2.1",
     "prosemirror-schema-basic": "^1.1.2",
     "prosemirror-schema-list": "^1.1.6",

yarn.lock

@@ -9447,15 +9447,7 @@ postcss-value-parser@^4.1.0, postcss-value-parser@^4.2.0:
   resolved "https://registry.yarnpkg.com/postcss-value-parser/-/postcss-value-parser-4.2.0.tgz#723c09920836ba6d3e5af019f92bc0971c02e514"
   integrity sha512-1NNCs6uurfkVbeXG4S8JFT9t19m45ICnif8zWLd5oPSZ50QnwMfK+H3jv408d4jw/7Bttv5axS5IiHoLaVNHeQ==
 
-postcss@^7.0.14, postcss@^7.0.5, postcss@^7.0.6:
-  version "7.0.39"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.39.tgz#9624375d965630e2e1f2c02a935c82a59cb48309"
-  integrity sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==
-  dependencies:
-    picocolors "^0.2.1"
-    source-map "^0.6.1"
-
-postcss@^8.2.1, postcss@^8.4.5:
+postcss@8.4.5, postcss@^8.2.1, postcss@^8.4.5:
   version "8.4.5"
   resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.5.tgz#bae665764dfd4c6fcc24dc0fdf7e7aa00cc77f95"
   integrity sha512-jBDboWM8qpaqwkMwItqTQTiFikhs/67OYVvblFFTM7MrZjt6yMKd6r2kgXizEbTTljacm4NldIlZnhbjr84QYg==
@@ -9464,6 +9456,14 @@ postcss@^8.2.1, postcss@^8.4.5:
     picocolors "^1.0.0"
     source-map-js "^1.0.1"
 
+postcss@^7.0.14, postcss@^7.0.5, postcss@^7.0.6:
+  version "7.0.39"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-7.0.39.tgz#9624375d965630e2e1f2c02a935c82a59cb48309"
+  integrity sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==
+  dependencies:
+    picocolors "^0.2.1"
+    source-map "^0.6.1"
+
 prelude-ls@^1.2.1:
   version "1.2.1"
   resolved "https://registry.yarnpkg.com/prelude-ls/-/prelude-ls-1.2.1.tgz#debc6489d7a6e6b0e7611888cec880337d316396"