Fix package lookup in Cargo metadata

[slonopotamus]

Broken by a33aee1

[mdsteele]

Thanks! Looks reasonable; please just fix the clippy error?

[stepbrobd]

I think this PR does not fix #138:

On aarch64-apple-darwin:

$ cat Cargo.toml
...
[package.metadata.bundle]
name = "Neovide"
identifier = "com.neovide.neovide"
icon = ["assets/neovide.ico"]
version = "0.10.0"
resources = []
copyright = "Copyright (c) Keith 2021. All rights reserved."
category = "Productivity"
short_description = "A simple GUI for Neovim."
long_description = """
This is a simple graphical user interface for Neovim. Where possible there are some graphical improvements, but it should act functionally like the terminal UI.
"""
osx_minimum_system_version = "10.11"
$ cargo bundle
error: No [package.metadata.bundle] section in Cargo.toml
^^^^^

I'm using cargo-bundle commit eb9fe1b0880c7c0e929a93edaddcb0a61cd3f0d4 introduced in NixOS/nixpkgs#222461.