Wii.Nunchuck and Wii.Classic can now be called with no parameters

Creating a new instance of Wii.Nunchuck or Wii.Classic with no parameters was throwing error.

e.g. this
```javascript
var nunchuk = new five.Wii.Nunchuk();
```

would result in this
```
/Users/derekwheelden/git/johnny-five/lib/wii.js:659
    freq: opts.freq || 100,
              ^
TypeError: Cannot read property 'freq' of undefined
```
why not just `_.result(opts, "freq", 100)`