Update readme.txt

Author: selul

readme.txt

@@ -2,7 +2,7 @@
 Contributors:  codeinwp,marius2012,marius_codeinwp,hardeepasrani,themeisle,Madalin_ThemeIsle,rozroz
 Tags: chart, charts, charting, graph, graphs, graphing, visualisation, visualise data, visualization, visualize data, HTML5, canvas, pie chart, line chart, bar chart, column chart, gauge chart, area chart, scatter chart, candlestick chart, geo chart, google visualization api
 Requires at least: 3.5
-Tested up to: 4.8.0
+Tested up to: 4.8
 Stable tag: trunk
 License: GPL v2.0 or later
 License URI: http://www.opensource.org/licenses/gpl-license.php