Fix bug when trying to retrieve city when error response occured

[tanraya]

I recently fixed a following error:

> Ipgeobase.lookup('127.0.0.1').city
NameError: uninitialized constant Ipgeobase::IpMetaData::Iconv

This error occurs when we get a 'not found' response from a web service:

<?xml version="1.0" encoding="windows-1251"?>
<ip-answer>
<ip value="127.0.0.1"><message>Not found</message></ip>
</ip-answer>

Please bump gem version after applying this PR.

[coveralls]

Coverage remained the same at 42.86% when pulling 0abeac4 on tanraya:fix-local-ip-bug into b9f4aaa on mokevnin:master.

[mokevnin]

thanks you!