test(sankey): raise the non-clamped case height to 1000

With 24 sink nodes the padding only stops clamping once the plot area
is ~1000px high (verified against the real layout: gap 27.3 at 900,
exactly 30 at 1000).

Author: CAOShurong

test/jasmine/tests/sankey_test.js

@@ -160,7 +160,7 @@ describe('sankey tests', function () {
 
             var fig = Lib.extendDeep({}, padMock);
             fig.layout.width = 480;
-            fig.layout.height = 880;
+            fig.layout.height = 1000;
             var gd = createGraphDiv();
             Plotly.newPlot(gd, fig)
                 .then(function() {