fix: debugger-ui incorrect path (react-native-community#226)

Summary:
---------

Missed this one while moving files around in react-native-community#201.
Fixes react-native-community#225


Test Plan:
----------

Verified locally on a clean project.

Author: thymikee

packages/cli/src/commands/server/middleware/MiddlewareManager.js

@@ -42,7 +42,7 @@ export default class MiddlewareManager {
   options: Options;
 
   constructor(options: Options) {
-    const debuggerUIFolder = path.join(__dirname, '..', 'util', 'debugger-ui');
+    const debuggerUIFolder = path.join(__dirname, '..', 'debugger-ui');
 
     this.options = options;
     this.app = connect()