Increased KeepAlive timeout threshold to be 3 keep alives

- This will also raise the timeout warn threshold
- I was unable to see scenarios when keep alive warn was being triggered
inaccurately but raising this threshold will ensure correctness

#1211

src/Microsoft.AspNet.SignalR.Client.JS/jquery.signalR.core.js

@@ -225,7 +225,7 @@
 
         disconnectTimeout: 40000, // This should be set by the server in response to the negotiate request (40s default)
 
-        keepAliveTimeoutCount: 2,
+        keepAliveTimeoutCount: 3,
 
         keepAliveWarnAt: 2 / 3, // Warn user of slow connection if we breach the X% mark of the keep alive timeout