Fix the Javascript Reverse router. Problem with default values.

The code generated in the Javascript reverse router in wrong for arguments with a default value.

Try:

```
GET  /       controllers.Application.index(limit: Int =? 10)
```

And try Js reverse router for this call:

```javascript
Router.controllers.Application.index()
```

It gives

```
/?10
```

Because anyway the default values are fixed server side, the client doesn't need to repeat the value. The simplest fix is to omit completely non-specified arguments that have a default value server side.