restore the received message (including \r\n in the end)

src/modem.rs

@@ -121,7 +121,7 @@ impl<UART: serial::Uart> Modem<UART> {
         //
         // This check here is tested on sim800l and works only because the modem has \r\n as CRLF.
         if line.ends_with("\r") {
-            Ok(line[0..line.len()-1].to_string())
+            Ok(format!("{}\n", line))
         }
         else {
             Err(ModemError::ReadError)