test(sankey): size the non-clamped case to genuinely fit node.pad

At 24 sink nodes a 900-high figure still clamps the padding (effective
gap 26.7 < 30); 880 was verified against the real layout to leave
enough room. Also fix the leftover single-arg spy in this test.

Author: CAOShurong

test/jasmine/tests/sankey_test.js

@@ -154,8 +154,8 @@ describe('sankey tests', function() {
             });
 
             var fig = Lib.extendDeep({}, padMock);
-            fig.layout.width = 700;
-            fig.layout.height = 900;
+            fig.layout.width = 480;
+            fig.layout.height = 880;
             var gd = createGraphDiv();
             Plotly.newPlot(gd, fig)
                 .then(function() {