Fix canvas counts

Author: dy

test/jasmine/tests/gl_plot_interact_test.js

@@ -1290,19 +1290,19 @@ describe('Test gl plot side effects', function() {
 
             return Plotly.plot(gd, data);
         }).then(function() {
-            countCanvases(1);
+            countCanvases(3);
 
             return Plotly.purge(gd);
         }).then(function() {
             countCanvases(0);
 
             return Plotly.plot(gd, data);
         }).then(function() {
-            countCanvases(1);
+            countCanvases(3);
 
             return Plotly.deleteTraces(gd, [0]);
         }).then(function() {
-            countCanvases(0);
+            countCanvases(3);
 
             return Plotly.purge(gd);
         }).then(done);