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

desktop/app/src/dispatcher/__tests__/plugins.node.js

@@ -33,7 +33,7 @@ beforeEach(() => {
 test('dispatcher dispatches REGISTER_PLUGINS', () => {
   dispatcher(mockStore, logger);
   const actions = mockStore.getActions();
-  expect(actions.map((a) => a.type)).toContain('REGISTER_PLUGINS');
+  expect(actions.map(a => a.type)).toContain('REGISTER_PLUGINS');
 });
 
 test('getDynamicPlugins returns empty array on errors', () => {