message: shell: fix docs build
  The docs build took the '\n' to literal.
diff: @@ -68,7 +68,7 @@ public:
  /**
  * @brief Send the shell message.
  *
  - * If shell_message.data string have not trailing '\n' symbol - it will be added.
  + * If shell_message.data string have not trailing newline - it will be added.
  *
  * If response data looks like not completed try to increase timeout value in request.
  *
  