fix: always close gridfs upload stream on finish (#2759)

Author: durran

src/gridfs-stream/upload.ts

@@ -67,6 +67,8 @@ export class GridFSBucketWriteStream extends Writable {
   };
   writeConcern?: WriteConcern;
 
+  /** @event */
+  static readonly CLOSE = 'close';
   /** @event */
   static readonly ERROR = 'error';
   /**
@@ -325,6 +327,7 @@ function checkDone(stream: GridFSBucketWriteStream, callback?: Callback): boolea
         return __handleError(stream, error, callback);
       }
       stream.emit(GridFSBucketWriteStream.FINISH, filesDoc);
+      stream.emit(GridFSBucketWriteStream.CLOSE);
     });
 
     return true;