Update version to v1.20.3

Source/GrasscutterTools/Properties/AssemblyInfo.cs

@@ -31,5 +31,5 @@ using System.Runtime.InteropServices;
 //可以指定所有这些值，也可以使用“生成号”和“修订号”的默认值
 //通过使用 "*"，如下所示:
 // [assembly: AssemblyVersion("1.0.*")]
-[assembly: AssemblyVersion("1.20.2")]
-[assembly: AssemblyFileVersion("1.20.2")]
+[assembly: AssemblyVersion("1.20.3")]
+[assembly: AssemblyFileVersion("1.20.3")]