MaxMind service cannot download CSV

As reported by @vogdb
```
$ ./sk/bin/cm location upgrade
Updating locations database…
Reading old country listing…
Downloading new country listing…
Reading new country listing…
Comparing both country listings…
Reading old region listing…
Downloading new region listing…
CM_Exception: Download of `http://dev.maxmind.com/static/csv/codes/maxmind/region.csv` failed in /home/vagrant/CM/library/CMService/MaxMind.php on line 764
    0. {main} ./sk/bin/cm:0
```

Probably they block requests without a User Agent? I think code should use `CM_Util::getContents()` anway instead of `@file_get_contents`?

@fauvel @vogdb something for you?