Downgrade date util for picker compatibility.

package.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "dependencies": {
-    "@date-io/date-fns": "^2.10.11",
+    "@date-io/date-fns": "1.x",
     "@material-ui/core": "^4.11.3",
     "@material-ui/icons": "^4.11.2",
     "@material-ui/lab": "^4.0.0-alpha.58",