update test to reflect the error that is now a warning

Author: Lindsay Carr

tests/testthat/tests-axis.R

@@ -42,7 +42,7 @@ test_that("axis reverse",{
 
   expect_true(gs2$side.3$reverse)
   expect_equal(xlim(gs2, side=3), c(10,1))
-  expect_error(ylim(gs2, side=3))
+  expect_warning(ylim(gs2, side=3))
 
 })