upgrade demo site to Next 12

Author: jpdriver

demo/.eslintrc

@@ -0,0 +1,4 @@
+{
+  "root": true,
+  "extends": "next/core-web-vitals"
+}

demo/.eslintrc.json

@@ -1,6 +1,6 @@
 {
   "name": "react-live-demo",
-  "version": "1.2.0",
+  "version": "1.3.0",
   "private": true,
   "license": "MIT",
   "scripts": {
@@ -13,18 +13,17 @@
   },
   "dependencies": {
     "formidable-oss-badges": "^0.3.6",
-    "next": "11.0.0",
-    "polished": "^4.1.3",
+    "next": "12.0.8",
     "react": "17.0.2",
     "react-dom": "17.0.2",
-    "react-live": "^2.2.3",
-    "styled-components": "^5.3.0"
+    "react-live": "^2.4.0",
+    "styled-components": "^5.3.3"
   },
   "devDependencies": {
     "babel-plugin-polished": "^1.1.0",
-    "babel-plugin-styled-components": "^1.12.0",
-    "eslint": "7.29.0",
-    "eslint-config-next": "11.0.0"
+    "babel-plugin-styled-components": "^2.0.2",
+    "eslint": "8.7.0",
+    "eslint-config-next": "12.0.8"
   },
   "engines": {
     "node": ">=12.0.0"