jquery.confirmable: Add a space between buttons

It should have always been there, my bad. Problems with lack of the
space:

* Languages with ligatures may decide to join the last letters of
  "Yes" with first letters of "No", producing a mess. (This was
  reported with a proposed solution as I0e6fcd83, I opted for doing
  this fix instead.)
* The "Yes" and "No" may be read together by screen readers, as
  "Yesno" (although I didn't test this), and similarly misinterpreted
  by other tools.
* The interface looks silly when copy-pasted.

Change-Id: I65c771fc22e105bf5978e6e4ee5068200f294b9e