Fix git stash-unapply example

The example for `git stash-unapply` starts with `git stash` which will
create a new stash and not apply a stash to the working copy.  The first
command should be either `git stash apply` (which is what I changed it
to) or `git stash apply stash@{0}` or a variant thereof.
Merge pull request #916 from sauerc/master

Fix git stash-unapply example