Bump src-cli MinimumVersion to 3.21.0
Created by: mrnugget
When downloading the latest version of src-cli from sourcegraph.com this
version here is used. And 3.20.0
is not the latest one.
We should default to immediately updating this when doing a release in
src-cli
. I'll add it to the src-cli
docs.
(Issue in which a user ran into this: https://github.com/sourcegraph/src-cli/issues/332)