stub out gl3d.plot in plot api test,

- so that tests can run on gl-less environments e.g. CircleCI.

Author: etpinard

test/jasmine/tests/plot_api_test.js

@@ -711,8 +711,12 @@ describe('Test plot api', function() {
                 }
             }];
 
+            spyOn(Plots.subplotsRegistry.gl3d, 'plot');
+
             Plotly.plot(gd, data);
 
+            expect(Plots.subplotsRegistry.gl3d.plot).toHaveBeenCalled();
+
             var contours = gd.data[0].contours;
 
             expect(contours.x.highlightColor).toBeUndefined();
@@ -736,8 +740,12 @@ describe('Test plot api', function() {
                 type: 'surface'
             }];
 
+            spyOn(Plots.subplotsRegistry.gl3d, 'plot');
+
             Plotly.plot(gd, data);
 
+            expect(Plots.subplotsRegistry.gl3d.plot).toHaveBeenCalled();
+
             var contours = gd.data[0].contours;
 
             expect(contours.x).toBeUndefined();