Fix some problems according to the 'classic' theme

Dear bkutil,
Recently I tried your bootstrap-theme and it looks perfect.
However, there seems to be some bugs leading to these two problems:
* The Dates are not showing of the Blog
* there're warnings saying "Layout 'nil' requested in atom.xml does not exist" every time you run 'rake generate'

After searching on Google, I found that the 'classic' theme has fixed these problems, see [Time element is empty for blog posted date](https://github.com/imathis/octopress/commit/73e540409ceb8bc18048b6a96a4b815fc303ea28). So I just copied there code and it performs correctly.

I really wish that everybody can enjoy this theme, so I make this attempt of a pulling request. And sorry if I have made any mistake because of lacking of experience.