cargo: bump version to 0.8.0-pre

Also, changed author from Carl to being more broad (as we have
many contributors and maintainers now).  This matches what is
used for crates in the rust-lang org.

Signed-off-by: Paul Osborne <osbpau@gmail.com>

Cargo.toml

@@ -2,8 +2,8 @@
 
 name        = "nix"
 description = "Rust friendly bindings to *nix APIs"
-version     = "0.7.1-pre"
-authors     = ["Carl Lerche <me@carllerche.com>"]
+version     = "0.8.0-pre"
+authors     = ["The nix-rust Project Developers"]
 homepage    = "https://github.com/nix-rust/nix"
 repository  = "https://github.com/nix-rust/nix"
 license     = "MIT"