Improve HTTP errors handling

### HTTP 401

```
$ ./bin/phantomas.js 'https://httpbin.org/basic-auth/foo/bar'
Error: Protocol error (Performance.getMetrics): Target closed.
```

### HTTP 404

```
./bin/phantomas.js http://127.0.0.1:8888/not_found 2>&1
Error: Navigation failed because browser has disconnected!
```