This is a patch to fix test failures. The latest version of broom (0.5.0) returns tibbles now. As the get_cox_res
function uses broom, the results were now being returned as tibbles. The test_get_cox_res.R uses expect_equal to test whether two data frames are equivalent, but this does not work for tibbles. This patch changes it such that the test first converts the tibbles to data frames to allow expect_equal to work.