fix for Highcharts export module: exporting.chartOptions

highcharts-exporting_fix-exporting-chartoptions.diff

diff --git a/vendor/exporting.src.js b/vendor/exporting.src.js
index d75f7da..75489a2 100644
--- a/vendor/exporting.src.js
+++ b/vendor/exporting.src.js
@@ -335,13 +335,15 @@ extend(Chart.prototype, {
 	exportChart: function (options, chartOptions) {
 		options = options || {};
 		
 		var chart = this,
 			chartExportingOptions = chart.options.exporting,
+			overrideOptions = chartExportingOptions ? (chartExportingOptions.chartOptions || {}) : {},
 			svg = chart.getSVG(merge(
 				{ chart: { borderRadius: 0 } },
 				chartExportingOptions,
+				overrideOptions,
 				chartOptions, 
 				{
 					exporting: {
 						sourceWidth: options.sourceWidth || chartExportingOptions.sourceWidth, // docs: option and parameter in exportChart()
 						sourceHeight: options.sourceHeight || chartExportingOptions.sourceHeight // docs