Fix typo (found by codespell)

Signed-off-by: Stefan Weil <sw@weilnetz.de>

README.md

@@ -325,7 +325,7 @@ _[Extensible Messaging and Presence Protocol](https://en.wikipedia.org/wiki/XMPP
   * [Candy](http://candy-chat.github.io/candy/) - Multi user XMPP client written in Javascript. ([Source Code](https://github.com/candy-chat/candy)) `MIT` `JavaScript`
   * [Converse.js](https://conversejs.org/) - A free and open-source XMPP chat client in your browser. ([Source Code](https://github.com/jcbrand/converse.js)) `MPLv2` `Javascript`
   * [Kaiwa](http://getkaiwa.com/) - Web based chat client in the style of common paid alternatives. ([Source Code](https://github.com/digicoop/kaiwa)) `MIT` `Javascript, NodeJS`
-  * [Kontalk](http://kontalk.org/) – Kontalk is an Open Source Messenger, similiar to WhatsApp (app for android only currently), including end-to-end encryption, server is based on Tigase XMPP Server. ([Source Code](https://github.com/kontalk)) `GPLv3`
+  * [Kontalk](http://kontalk.org/) – Kontalk is an Open Source Messenger, similar to WhatsApp (app for android only currently), including end-to-end encryption, server is based on Tigase XMPP Server. ([Source Code](https://github.com/kontalk)) `GPLv3`
   * [Salut à Toi](http://www.salut-a-toi.org/) - Multipurpose, multi frontend, libre and decentralised communication tool. ([Source Code](http://repos.goffi.org/sat)) `AGPLv3` `Python`
     * [Libervia](http://wiki.goffi.org/wiki/Libervia/en) - Web frontend from Salut à Toi. ([Source Code](http://repos.goffi.org/libervia)) `AGPLv3` `Python`