set netlify to use Node 12

Author: jpdriver

demo/netlify.toml

@@ -0,0 +1,2 @@
+[build.environment]
+  NODE_VERSION = 12

demo/package.json

@@ -25,5 +25,8 @@
     "babel-plugin-styled-components": "^1.12.0",
     "eslint": "7.29.0",
     "eslint-config-next": "11.0.0"
+  },
+  "engines": {
+    "node": ">=12.0.0"
   }
-}
+}