Change naming of layers with zindex

Author: Farkites

src/plots/cartesian/index.js

@@ -221,7 +221,7 @@ function plotOne(gd, plotinfo, cdSubplot, transitionOpts, makeOnCompleteCallback
             var categories = Registry.modules[name].categories;
 
             if(categories.svg) {
-                var className = (_module.layerName || name + 'layer') + (zindex ? '-' + z : '');
+                var className = (_module.layerName || name + 'layer') + (zindex ? Number(z) + 1 : '');
                 var plotMethod = _module.plot;
 
                 // plot all visible traces of this type on this subplot at once

test/image/mocks/zindex-scatter-image.json

@@ -4,7 +4,8 @@
         "type": "scatter",
         "y": ["E", "F", "G", "H"],
         "x": ["A", "B", "C", "D"]
-        }, {
+    }, 
+    {
         "type": "image",
         "zmax": [1, 1, 1],
         "x0": "B",