我可以用signalr 2吗?如果我使用的是Microsoft.Bcl，则使用。net 4.0。(从1升级。在。net 4.0 x)

I know that Signalr 2.x was design for .NET 4.5. Unfortunately, we cannot update our production server to .NET 4.5. If I include the I know that Signalr 2.x was design for .NET 4.5