add a few more invisible trace in gl2d mock

Author: etpinard

test/image/mocks/gl2d_scatter-marker-line-colorscales.json

@@ -192,6 +192,18 @@
         },
         {
             "type": "scattergl"
+        },
+        {
+            "type": "scattergl",
+            "x": [1,2,3],
+            "y": [2,1,2],
+            "visible": false
+        },
+        {
+            "type": "scattergl",
+            "x": [1,2,3],
+            "y": [2,1,2],
+            "visible": "legendonly"
         }
     ],
     "layout": {