when customer replace ${version} with 4.0.4 , download file will miss pd, tidb,tikv package.

[yilongrong]

General Question

when customer use under command download package, if ${version} replace to 4.0.4 ,it will miss some package.
customer must use v4.0.4 to download package .
tiup mirror clone tidb-community-server-${version}-linux-amd64 ${version} --os=linux --arch=amd64

[lucklove]

We should limit the user input of the version, which must start with a 'v'

[lonng]

@lucklove Or we add the v prefix automatically.