Fixing help annotation on serial.redirect

Code currently points to help at https://codethemicrobit.com/reference/serial/redirect but the working url is https://codethemicrobit.com/reference/serial/redirect-to so fixed the help annotation

libs/microbit/serial.cpp

@@ -61,11 +61,11 @@ namespace serial {
     * @param baud the new baud rate. eg: 115200
     */
     //% weight=10
-    //% help=serial/redirect
+    //% help=serial/redirect-to
     //% blockId=serial_redirect block="serial redirect to|TX %tx|RX %rx|at baud rate %rate"
     //% blockExternalInputs=1
     void redirect(SerialPin tx, SerialPin rx, BaudRate rate) {
       uBit.serial.redirect((PinName)tx, (PinName)rx);
       uBit.serial.baud((int)rate);
     }
-}
+}