Add missing Server import

Summary: Not sure why Flow was okay with this before.

Reviewed By: danielbuechele

Differential Revision: D15601506

fbshipit-source-id: a211bb373061d1481dbc6748d4e061a980cd0278

src/utils/CertificateProvider.js

@@ -6,6 +6,7 @@
  */
 
 import type {Logger} from '../fb-interfaces/Logger';
+import Server from '../server';
 import {promisify} from 'util';
 const fs = require('fs');
 import {