Using Dygraphs I can setup a plugin on initial load

```
plugins: [
    new Dygraph.Plugins.Crosshair({
    direction: "both"
    })
]

```

But I don't seem to be able to change the direction parameter with `updateOptions`

I tried

```
var pluginOpt = {};

pluginOpt = { 

    plugins: [
        new Dygraph.Plugins.Crosshair({
        direction: "neither"
        })
    ]

 };

 g.updateOptions({
      plugins: pluginOpt
 });

```

Also tried just passing `direction` , both fail silently, with nothing updated