Added replace parameter for setText

Requires https://github.com/admc/wd/pull/333 to be pulled first.

I also want to create a test for this in keyboard-specs.js but I can add that in another pull. 

Tested with the wd.js change and it works for me.
I don't think we need a comment explaining that `array.join('');` converts an array into a string (that's just the convention in javascript), but I do think it could be meaningful to have a comment like this explaining why we need the conversion:

```js
// spec says value attribute is an array of strings; let's turn it into one string
```