index.md: replace qwebirc link with kiwi button & enable Travis CI.

* SSL is used for connecting to freenode.
* No captcha.
* Looks nicer than some link.
* KiwiIRC looks nicer than qwebirc.

The button looks like this: [![Visit our IRC channel](https://kiwiirc.com/buttons/chat.freenode.net/%23feminist.png)](https://kiwiirc.com/client/chat.freenode.net:+6697/##feminist)

I think that my vimrc also replaced tabs with spaces or converted to Unix-line-endings or both or something as I only changed one line.

I am now worried if I broke the build, so I enabled Travis with instructions from https://help.github.com/articles/troubleshooting-github-pages-build-failures#configuring-a-third-party-service-to-display-jekyll-build-error-messages .