Console error reported for serial_redirect

[martinwork]

Describe the bug

In a new project, the first opening of the Serial toolbox panel triggers a browser console error

I think this may be because the rate parameter description "e.g." is picked up as a default value

pxt-microbit/libs/core/serial.cpp

Line 161 in ee22e99

* @param rate the new baud rate. eg: 115200

pxt-microbit/libs/core/shims.d.ts

Line 1068 in ee22e99

* @param rate the new baud rate. eg: 115200

To Reproduce
Steps to reproduce the behavior:

1. Go to https://makecode.microbit.org/
2. Create a new project and open the browser console
3. Open the Serial toolbox panel
4. See error

Expected behavior
A correct default value is specified

Screenshots

micro:bit version (please complete the following information):
not hardware related

Desktop (please complete the following information):

• OS: [e.g. iOS] Windows
• Browser [e.g. chrome, safari] Chrome
• Version [e.g. 22]