Fix logging reconnect errors after a successful login (#592)

A logging call on stream error code 515 was missing the format specifier for
the reconnection error. This commit adds the specifier.

Signed-off-by: Carlos Torres <torr.ca@mailgw.com>

connectionevents.go

@@ -28,7 +28,7 @@ func (cli *Client) handleStreamError(node *waBinary.Node) {
 			cli.Disconnect()
 			err := cli.Connect()
 			if err != nil {
-				cli.Log.Errorf("Failed to reconnect after 515 code:", err)
+				cli.Log.Errorf("Failed to reconnect after 515 code: %v", err)
 			}
 		}()
 	case code == "401" && conflictType == "device_removed":