yarn: Upgrade packages

- react: 16.13.1
- react-admin: 3.4.0
- prettier: 2.0.0

Change-Id: Ibbd4ff2bd8054a7086d194229ec732c1a256579c

.prettierrc

@@ -6,5 +6,6 @@
   "singleQuote": false,
   "trailingComma": "es5",
   "bracketSpacing": true,
-  "jsxBracketSameLine": false
+  "jsxBracketSameLine": false,
+  "arrowParens": "avoid",
 }