add title in header of rss.xml

I got an error when commit feed.xml :
> Page build failed. For more information, see https://help.github.com/articles/using-jekyll-with-pages#troubleshooting.

util I add title in header:

    ---
    layout: none
    title: none
    ---

I don't know whether it is nessary, please ignore this pull request if not.

thank you for your feeds template.