Retry on response code 429 (#454)

Author: dejan2k

LeanplumSDK/LeanplumSDK/Classes/Managers/Networking/LPRequestSender.m

@@ -283,6 +283,7 @@ - (void)sendRequests
             // Retry on 500 and other network failures.
             NSInteger httpStatusCode = completedOperation.HTTPStatusCode;
             if (httpStatusCode == 408
+                || httpStatusCode == 429
                 || (httpStatusCode >= 500 && httpStatusCode < 600)
                 || err.code == NSURLErrorBadServerResponse
                 || err.code == NSURLErrorCannotConnectToHost