Try to fix against the failed image test

Author: hy9be

src/plot_api/plot_api.js

@@ -206,7 +206,7 @@ Plotly.plot = function(gd, data, layout, config) {
             if(trace.visible !== true || !trace._module.colorbar) {
                 Plots.autoMargin(gd, 'cb' + trace.uid);
             }
-            else if(Plots.traceIs(trace, 'markerColorscale') || Colorbar.hasColorbar(trace)) {
+            else if(Plots.traceIs(trace, 'markerColorscale') || Plots.traceIs(trace, 'parcoords') || Colorbar.hasColorbar(trace)) {
                 trace._module.colorbar(gd, cd);
             }
         }

src/traces/parcoords/index.js

@@ -19,7 +19,7 @@ Parcoords.colorbar = require('./colorbar');
 Parcoords.moduleType = 'trace';
 Parcoords.name = 'parcoords';
 Parcoords.basePlotModule = require('./base_plot');
-Parcoords.categories = ['gl', 'noOpacity', 'markerColorscale'];
+Parcoords.categories = ['gl', 'noOpacity'];
 Parcoords.meta = {
     description: [
         'Parallel coordinates for multidimensional exploratory data analysis.',