$.fn.val.call([el]) breaks other jQuery plugins

The 3.2.2 form_params plugin, line 116, uses this:

```
$.fn.val.call([el])
```

Because the array is not a jQuery object, it breaks other plugins (e.g., tinymce) that override val and expect a jQuery object. Changing it to:

```
$(el).val()
```

fixes the problem.
