Fixed displayed domain for xip.io from xip.ip

The link was correct but the domain that was displayed was xip.ip. This commit fixes that mistake.

README.md

@@ -374,7 +374,7 @@ Only main chapters:
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://dnsdumpster.com/"><b>DNSdumpster</b></a> - dns recon & research, find & lookup dns records.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://dnstable.com/"><b>DNS Table online</b></a> - search for DNS records by domain, IP, CIDR, ISP.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://ptrarchive.com/"><b>PTRarchive.com</b></a> - this site is responsible for the safekeeping of historical reverse DNS records.<br>
-&nbsp;&nbsp;:small_orange_diamond: <a href="http://xip.io/"><b>xip.ip</b></a> - wildcard DNS for everyone.<br>
+&nbsp;&nbsp;:small_orange_diamond: <a href="http://xip.io/"><b>xip.io</b></a> - wildcard DNS for everyone.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://intodns.com/"><b>intoDNS</b></a> - DNS and mail server health checker.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://leafdns.com/"><b>Leaf DNS</b></a> - comprehensive DNS tester.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://ceipam.eu/en/dnslookup.php"><b>dnslookup (ceipam)</b></a> - one of the best DNS propagation checker (and not only).<br>