message: Update API doc URL for Cargo
  Closes
diff: @@ -7,7 +7,7 @@ authors = ["Yehuda Katz <wycats@gmail.com>",
  license = "MIT/Apache-2.0"
  homepage = "https://crates.io"
  repository = "https://github.com/rust-lang/cargo"
  -documentation = "http://doc.crates.io/cargo"
  +documentation = "https://docs.rs/cargo"
  description = """
  Cargo, a package manager for Rust.
  """
  