The `rls-preview` component on beta is "corrupted"

[alexcrichton]

With the second release of the beta toolchain we've got the rls-preview component now (not the rls) and it looks like it's almost working! The only piece that seems off is:

$ rustup component add rls-preview --toolchain beta
info: downloading component 'rls-preview'
info: installing component 'rls-preview'
info: rolling back changes
error: component manifest for 'rls-preview' is corrupt

cc @nrc

Note that I've tagged this as a beta regressoin but it's not actually a regression, it's just there to make sure we keep looking at it.