Update readme.txt

WordPress tested up to version updated

Author: vytisbulkevicius

readme.txt

@@ -2,7 +2,7 @@
 Contributors: codeinwp,themeisle,marius2012,marius_codeinwp,hardeepasrani,rozroz,Madalin_ThemeIsle
 Tags: tables, charts, pie, visualization, graphs
 Requires at least: 5.2
-Tested up to: 6.3
+Tested up to: 6.4
 Requires PHP: 7.4
 Stable tag: trunk
 License: GPL v2.0 or later