C#8->C#11

Author: ryu-s

BigoSitePlugin/BigoSitePlugin.csproj

@@ -2,7 +2,6 @@
   <PropertyGroup>
     <UseWPF>true</UseWPF>
     <TargetFramework>net60-windows</TargetFramework>
-    <LangVersion>8.0</LangVersion>
     <Configurations>Release;Beta;Alpha;Debug</Configurations>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">