"non-standard" license-file

[cuviper]

Commit 11d53ba removed license from Cargo.toml in favor of license-file, but this causes crates.io to show it as a "non-standard" license. I would recommend going the other way, using only the license field, but do make sure the file is still included in the package (cargo package --list).

See also: rust-lang/cargo#8537