honor mesh3d 'facecolor' before 'vertexcolor'

- as describe in the attribute descriptions

Author: etpinard

src/traces/mesh3d/attributes.js

@@ -125,7 +125,7 @@ module.exports = {
         description: 'Sets the color of the whole mesh'
     },
     vertexcolor: {
-        valType: 'data_array',  // FIXME: this should be a color array
+        valType: 'data_array',
         role: 'style',
         description: [
             'Sets the color of each vertex',

src/traces/mesh3d/defaults.js

@@ -82,8 +82,8 @@ module.exports = function supplyDefaults(traceIn, traceOut, defaultColor, layout
     else {
         traceOut.showscale = false;
 
-        if('vertexcolor' in traceIn) coerce('vertexcolor');
-        else if('facecolor' in traceIn) coerce('facecolor');
+        if('facecolor' in traceIn) coerce('facecolor');
+        else if('vertexcolor' in traceIn) coerce('vertexcolor');
         else coerce('color', defaultColor);
     }