Fix "TypeError: an integer is required" error on Python 3.5.2
diff --git a/serial/threaded/__init__.py b/serial/threaded/__init__.py
index 325d4a3..d4a4ab4 100644
--- a/serial/threaded/__init__.py
+++ b/serial/threaded/__init__.py
@@ -105,7 +105,7 @@
                 self.handle_packet(self.packet)
                 del self.packet[:]
             elif self.in_packet:
-                self.packet.append(byte)
+                self.packet.extend(byte)
             else:
                 self.handle_out_of_packet_data(byte)