Merge branch 'master' of https://github.com/SciSharp/BotSharp into features/add-pdf-upload

Author: Jicheng Lu

src/Plugins/BotSharp.Plugin.MetaGLM/BotSharp.Plugin.MetaGLM.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFramework>netstandard2.1</TargetFramework>
     <Nullable>enable</Nullable>
-    <LangVersion>$(LangVersion)</LangVersion>
+    <LangVersion>12.0</LangVersion>
     <VersionPrefix>$(BotSharpVersion)</VersionPrefix>
     <GeneratePackageOnBuild>$(GeneratePackageOnBuild)</GeneratePackageOnBuild>
     <GenerateDocumentationFile>$(GenerateDocumentationFile)</GenerateDocumentationFile>