Minor doc fix in skipping.txt.  Also submitted at Github before I realised that this was the master repo.  Will close over there.
correct documentation typo
doc: fix desc for `parametrize`

 - the parameter is called `expected`, not `output`
 - s/that that/that/
Merged in lakka/pytest//minor-doc-fix-in-skippingtxt-also-submi-1387492852421 (pull request #94)

Minor doc fix in skipping.txt.  Also submitted at Github before I realised that this was the master repo.  Will close over there.