test: add colorbars to colorscale_contraint mock

Author: etpinard

test/image/baselines/colorscale_constraint.png

@@ -6,7 +6,12 @@
       "color": [1,2,3,4],
       "cmin": 2,
       "cmax": 3,
-      "showscale": true
+      "colorbar": {
+        "title": "trace 0",
+        "len": 0.3,
+        "y": 0,
+        "yanchor": "bottom"
+      }
     }
   }, {
     "x": [1,2,3,4,5],
@@ -15,7 +20,12 @@
       "color": [1,2,3,4],
       "cmin": 1,
       "cmax": 4,
-      "showscale": false
+      "colorbar": {
+        "title": "trace 1",
+        "len": 0.3,
+        "y": 0.3,
+        "yanchor": "bottom"
+      }
     }
   }, {
     "x": [1,2,3,4],
@@ -24,7 +34,12 @@
     "marker": {
       "color": [0,0,0,0],
       "size": 10,
-      "showscale": false
+      "colorbar": {
+        "title": "trace 2",
+        "len": 0.3,
+        "y": 0.6,
+        "yanchor": "bottom"
+      }
     }
   }],
   "layout": {