tests: use positive revision numbers in test-strip-cross.t
It took me a long time to realize that '-r -1' was pulling revision -1
because I didn't even notice the minus sign until I tried changing the
revision number. The order of arguments doesn't matter, so I changed
from decreasing order to increasing while at it.
Differential Revision: https://phab.mercurial-scm.org/D6790
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors