travis.yml uses 'default' not 'compat' build

The `travis.yml` file passes a env.variable `BUILD`, example:

```
    - BROWSER='chrome_linux'    BUILD='default'
    - BROWSER='firefox_linux'   BUILD='default'
    - BROWSER='chrome_linux'    BUILD='nocompat'
    - BROWSER='firefox_linux'   BUILD='nocompat'
```

and the gruntfile was looking for a `compat` instead of `default`.