Fix issue for HttpClient connection closed unexpectedly error after events submission. (#207)

* Recording exception details in logs to identify issues easier.

* Fix issue for HttpClient connection close error after events submission.

Author: edwardmeng

src/Exceptionless/Submission/DefaultSubmissionClient.cs

@@ -150,6 +150,7 @@ protected virtual HttpClient CreateHttpClient(ExceptionlessConfiguration config)
                 handler.Proxy = config.Proxy;
 
             var client = new HttpClient(handler, true);
+            client.DefaultRequestHeaders.ConnectionClose = true;
             client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
             client.DefaultRequestHeaders.ExpectContinue = false;
             client.DefaultRequestHeaders.UserAgent.ParseAdd(config.UserAgent);