yarn: Upgrade packages

- babel: 7.13
- material-ui: 4.11
- prettier: 2.2
- react-admin: 3.14

Change-Id: I26ab6d9d75110f3522282b83cd1131af98b8c43c

src/App.test.js

@@ -1,5 +1,5 @@
 import React from "react";
-import { TestContext } from "react-admin";
+import { TestContext } from "ra-test";
 import { shallow } from "enzyme";
 import App from "./App";
 

src/components/LoginPage.test.js

@@ -1,5 +1,5 @@
 import React from "react";
-import { TestContext } from "react-admin";
+import { TestContext } from "ra-test";
 import { shallow } from "enzyme";
 import LoginPage from "./LoginPage";