blockDomains: handle redirects

``--no-externals`` fails when initial redirect changes the domain

Fixes #197

```
$ phantomas --url http://google.com --no-externals --verbose --modules blockDomains

...
20:32:05.307 Block domains: assuming "www.google.pl" to be the main domain
20:32:05.651 Blocked request: <http://clients1.google.pl/generate_204>
...
phantomas v0.11.1 metrics for <http://www.google.pl/...>:
```