use fs instead of fs/promises for compatibility with older vscode ver…

…sions

lib/flowLSP/utils/getVerifiedFlowBinPath.js

@@ -2,14 +2,16 @@
 import Logger from './Logger';
 import importFresh from './importFresh';
 import getExtensionPath from './getExtentionPath';
-// $FlowFixMe Flow doesn't recognize the fs/promises node module
-import { readFile, readdir, access } from 'fs/promises';
+import { promises } from 'fs';
 import { createReadStream } from 'fs';
 import path from 'path';
 // $FlowFixMe Flow doesn't recognize crypto.verify
 import { verify, createHash } from 'crypto';
 import { window } from 'vscode';
 
+// fs/promises
+const { readFile, readdir, access } = promises;
+
 function getFlowBinDirPrefixForPlatform(): null | string {
     return process.platform === 'darwin'
                 ? 'flow-osx-v' :
@@ -44,7 +46,7 @@ async function getShasums(flowBinModulePath: string, logger: Logger): Promise<Bu
     try {
         // try veryifying against SHASUM256.txt.sign
         const shasums = await readFile(path.join(flowBinModulePath, 'SHASUM256.txt'));
-        const shasumsSignatureBase64 = await readFile(path.join(flowBinModulePath, 'SHASUM256.txt.sign'), { encoding: 'ascii' });
+        const shasumsSignatureBase64 = await readFile(path.join(flowBinModulePath, 'SHASUM256.txt.sign'), 'ascii' );
         const shasumsSignature = Buffer.from(shasumsSignatureBase64, 'base64');
         const publicKey = await readFile(path.join(extensionPath, 'signing.pem'));
         if (!verify('sha256', shasums, publicKey, shasumsSignature)) {