galleria template: Use striptags with in title tag

Hey Simon,

Thanks for working on sigal. I really like it - took me just few minutes to learn how to use sigal to do exactly what I want. 

Only issue I had was that I want part of the title in red so I had to use html span tag in index.md. Works great except the tag is shown in the title bar of the web browser, this one line pull request fixes that.

Thanks,
Lucas