Upgrade Prettier from 1.17 to 2.0.2.

Summary:
This gets us on the latest Prettier 2.x:
https://prettier.io/blog/2020/03/21/2.0.0.html

Notably, this adds support for TypeScript 3.8,
which introduces new syntax, such as `import type`.

Reviewed By: zertosh

Differential Revision: D20636268

fbshipit-source-id: fca5833d003804333a05ba16325bbbe0e06d6c8a

RNTester/js/examples/ToastAndroid/ToastAndroidExample.android.js

@@ -129,7 +129,7 @@ exports.description =
 exports.examples = [
   {
     title: 'Basic toast',
-    render: function(): React.Element<typeof ToastExample> {
+    render: function (): React.Element<typeof ToastExample> {
       return <ToastExample />;
     },
   },