Do not use 'ratio' in test_slic.py either

skimage/segmentation/tests/test_slic.py

@@ -80,7 +80,8 @@ def test_gray_3d():
     img += 0.001 * rnd.normal(size=img.shape)
     img[img > 1] = 1
     img[img < 0] = 0
-    seg = slic(img, sigma=0, n_segments=8, ratio=20.0, multichannel=False)
+    seg = slic(img, sigma=0, n_segments=8, compactness=20.0,
+               multichannel=False)
 
     assert_equal(len(np.unique(seg)), 8)
     for s, c in zip(slices, range(8)):