Fix artemis fleet documentation. (#505)

It said 'toit' instead of 'artemis'.

This page is copied over from the Artemis repository on each Artemis
release, but we want to fix the documentation before the next release.

docs/getstarted/fleet/reliability.mdx

@@ -48,10 +48,10 @@ firmware-envelope: x64-linux
 containers: {}
 ```
 
-The max-offline value can also be set using the `toit` CLI:
+The max-offline value can also be set using the `artemis` CLI:
 
 ```bash
-toit device -d DEVICE-ID set-max-offline 1h
+artemis device -d DEVICE-ID set-max-offline 1h
 ```
 
 This configuration change is not permanent and will be lost with the next firmware update.