Update Abp.AspNetCore.SignalR to 3.4.0-preview2

Author: acjh

aspnet-core/src/AbpCompanyName.AbpProjectName.Web.Core/AbpCompanyName.AbpProjectName.Web.Core.csproj

@@ -49,7 +49,7 @@
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp2.0' ">
-    <PackageReference Include="Abp.AspNetCore.SignalR" Version="3.3.0-preview1" />
+    <PackageReference Include="Abp.AspNetCore.SignalR" Version="3.4.0-preview2" />
   </ItemGroup>
 
 </Project>