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/utils/js-client/webviewImpl.js

@@ -39,7 +39,7 @@ class FlipperWebviewBridgeImpl extends FlipperBridge {
   subscribe = (
     plugin: FlipperPluginID,
     method: FlipperMethodID,
-    handler: (any) => void,
+    handler: any => void,
   ) => {
     this._subscriptions.set(plugin + method, handler);
   };