Update mongodb to the latest version 🚀 (#5914)

* fix(package): update mongodb to version 3.3.0

* chore(package): update lockfile package-lock.json

* Fix tests

* Fix GraphQL tests for read preference

* Fix mongo adapter deprecation notice

* Fix the way the connections are checked, return promise when shutting down mongo

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -146,6 +146,7 @@ export class MongoStorageAdapter implements StorageAdapter {
     this._collectionPrefix = collectionPrefix;
     this._mongoOptions = mongoOptions;
     this._mongoOptions.useNewUrlParser = true;
+    this._mongoOptions.useUnifiedTopology = true;
 
     // MaxTimeMS is not a global MongoDB client option, it is applied per operation.
     this._maxTimeMS = mongoOptions.maxTimeMS;
@@ -203,9 +204,9 @@ export class MongoStorageAdapter implements StorageAdapter {
 
   handleShutdown() {
     if (!this.client) {
-      return;
+      return Promise.resolve();
     }
-    this.client.close(false);
+    return this.client.close(false);
   }
 
   _adaptiveCollection(name: string) {

src/ParseServer.js

@@ -117,8 +117,12 @@ class ParseServer {
   handleShutdown() {
     const { adapter } = this.config.databaseController;
     if (adapter && typeof adapter.handleShutdown === 'function') {
-      adapter.handleShutdown();
+      const promise = adapter.handleShutdown();
+      if (promise instanceof Promise) {
+        return promise;
+      }
     }
+    return Promise.resolve();
   }
 
   /**