`emsdk install 2.0.20-lto` does not work

Hi,

I already posted this as a reply to [your Tweet](https://twitter.com/emscripten/status/1392149058945314819) - so please forgive me for posting this twice, but I'm really excited about this news. I would like to test the new 2.0.20-lto builds and see if I can reduce my build times, which are currently at more than 24 hours for one of my build setups.

Unfortunately I get the following error when trying the command from the tweet:

```bash
$ emsdk install 2.0.20-lto
Fetching emscripten-releases repository...
Repository 'https://chromium.googlesource.com/emscripten-releases' already cloned to directory '/usr/lib/emsdk/releases', skipping.
Fetching latest changes to the branch 'master' for '/usr/lib/emsdk/releases'...
Already up to date.
Successfully updated and checked out branch 'master' on repository '/usr/lib/emsdk/releases'
Current repository version: "Tue, 11 May 2021 19:36:36 +0000 f4564474f39d09cb7245c5ea8010665e3f80c082"
Error: No tool or SDK found by name '2.0.20-lto'.
```