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

Libraries/Core/Devtools/parseErrorStack.js

@@ -57,7 +57,7 @@ function parseErrorStack(e: ExtendedError): Array<StackFrame> {
     ? e.stack
     : global.HermesInternal
     ? convertHermesStack(parseHermesStack(e.stack))
-    : stacktraceParser.parse(e.stack).map(frame => ({
+    : stacktraceParser.parse(e.stack).map((frame) => ({
         ...frame,
         column: frame.column != null ? frame.column - 1 : null,
       }));