fix js lint error

lib/browser/guest-window-manager.js

@@ -120,8 +120,9 @@ const createGuest = function (embedder, url, frameName, options, postData) {
     // The above code would not work if a navigation to "about:blank" is done
     // here, since the window would be cleared of all changes in the next tick.
     const loadOptions = {}
-    if (postData)
+    if (postData) {
       loadOptions.postData = postData
+    }
     guest.loadURL(url, loadOptions)
   }