Replace alpha state by beta state

[GuillaumeGomez]

Fixes #24060.

[rust-highfive]

r? @brson

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[GuillaumeGomez]

r? @steveklabnik

[MatejLach]

Is Cargo following Rust in lockstep?
Last time I checked it was still considered alpha.
@GuillaumeGomez Also I suspect that it is "a beta", rather than "an beta", but I am not a native English speaker myself, so I could be wrong.

[GuillaumeGomez]

No, you're totally right, it's "a" and not "an".

For Cargo state, I thought it was following the rust state. We'll see what they'll say about that.

[steveklabnik]

How about, "pre-1.0" for now?

[GuillaumeGomez]

@steveklabnik: I change that !

[GuillaumeGomez]

@steveklabnik: Done.

[steveklabnik]

You picked up a sub module there

[GuillaumeGomez]

@steveklabnik: fixed !

[alexcrichton]

@bors: r+ 92d0026 rollup