update supported .NET version

Author: Mark-Dynamsoft

programming/dotnet/index.md

@@ -33,7 +33,7 @@ If you are new to Dynamsoft Barcode Reader .NET Edition, follow the [`User Guide
 
 - Supported .NET versions
   - .NET Framework 3.5 and above
-  - .NET 6, 7, 8
+  - .NET 6 and above
 
 > [!NOTE]
 > Other architectures and operating systems, such as ESP32, MIPS, FreeRTOS, and Micrium uC/OS, are not supported.