FIX: Browser version parsing when only 'latest' specified

In .zuul.yml if you specify just:

- name: iphone
  version: latest

It will accidentally return something like this when running zuul:

```
zuul:sauce add undefined undefined undefined +0ms
- testing: undefined @ undefined:
```

Correct it so it correctly run the test:

```
zuul:sauce add iphone 6.1 Mac 10.8 +0ms
- testing: iphone @ iOS: 6.1
```