csv example bug fix

xchart-demo/CSV/CSVChartRowsExport/series1.csv

-1,2,3
-12,34,56
-4,12,21
+1.0,2.0,3.0
+12.0,34.0,56.0
+4.0,12.0,21.0

xchart-demo/src/main/java/com/xeiam/xchart/standalone/CSVChartRows.java

@@ -31,7 +31,7 @@ public class CSVChartRows {
     // import chart from a folder containing CSV files
     Chart chart = CSVImporter.getChartFromCSVDir("./CSV/CSVChartRows/", DataOrientation.Rows, 600, 400);
 
-    CSVExporter.writeCSVRows(chart.getSeriesMap().get(0), "./CSV/CSVChartRowsExport/");
+    CSVExporter.writeCSVRows(chart.getSeriesMap().get("series1"), "./CSV/CSVChartRowsExport/");
 
     // Show it
     new SwingWrapper(chart).displayChart();