Fix the example provided in README to compile and work.

I've tested the patched example this way:
* building librdns
```
% mkdir build && cd build && cmake .. && make
```
* building the example from README
```
% vim test.c
% cc -g -c -I /usr/local/include -I ../include test.c
% cc -g test.o librdns_static.a -L /usr/local/lib -lev
```
* Finally launching the test:
```
% ./a.out ::1 53      
got result for host: google.com
got result for host: github.com
got result for host: www.ник.рф
got result for host: kernel.org
got result for host: freebsd.org
%
```

For info:
```
% uname -a
FreeBSD kaworu.ch 10.0-RELEASE-p9 FreeBSD 10.0-RELEASE-p9 #0: Mon Sep 15 14:35:52 UTC 2014     root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
% cc --version
FreeBSD clang version 3.3 (tags/RELEASE_33/final 183502) 20130610
Target: x86_64-unknown-freebsd10.0
Thread model: posix
```