properly call callback on close

Author: flotwig

lib/stdio-wrapper.js

@@ -78,9 +78,10 @@ class StdioWrapper extends EventEmitter {
         this._pendingMessage = buffer.toString(undefined, start);
     }
 
-    close() {
+    close(callback) {
         this._pipeWrite = null;
         removeEventListeners(this._eventListeners);
+        callback();
     }
 }