Prevent table from extending parent width

The table containing the _Permalink style examples_ [in the docs](http://jekyllrb.com/docs/permalinks/#permalink-style-examples) extends the width of the content container.

The solution I propose is a bit dirty, because I remove `permalink: ` in the left column to make the table fit.

Another way would be using `white-space: normal;` for code inside tables. That would lead to _ugly_ line-breaks within the code.

What do you think?
Merge pull request #2424 from kleinfreund/patch-2