fsPromises.appendFile's options are optional

Summary:
https://nodejs.org/api/fs.html#fspromisesappendfilepath-data-options

Changelog: [libdef] Make some `options` parameters in node's `fsPromises` optional

Reviewed By: gkz

Differential Revision: D33659690

fbshipit-source-id: b4d499eb265032949821238c1bd8b9ea45ce57a9

lib/node.js

@@ -1327,7 +1327,7 @@ declare module "fs" {
   declare type FSPromisePath = string | Buffer | URL;
   declare type FSPromise = {
     access(path: FSPromisePath, mode?: number): Promise<void>,
-    appendFile(path: FSPromisePath | FileHandle, data: string | Buffer, options: WriteOptions | string): Promise<void>,
+    appendFile(path: FSPromisePath | FileHandle, data: string | Buffer, options?: WriteOptions | string): Promise<void>,
     chmod(path: FSPromisePath, mode: number): Promise<void>,
     chown(path: FSPromisePath, uid: number, gid: number): Promise<void>,
     copyFile(src: FSPromisePath, dest: FSPromisePath, flags?: number): Promise<void>,
@@ -1347,7 +1347,7 @@ declare module "fs" {
       mode?: number,
       ...
     }): Promise<void>,
-    mkdtemp(prefix: string, options: EncodingOptions): Promise<string>,
+    mkdtemp(prefix: string, options?: EncodingOptions): Promise<string>,
     open(path: FSPromisePath, flags?: string | number, mode?: number): Promise<FileHandle>,
     read<T: Buffer | Uint8Array>(
       filehandle: FileHandle,