Fix warning about default_features being deprecated

[gretchenfrage]

When cargo check is run on master, the following warning is logged:

warning: `default_features` is deprecated in favor of `default-features` and will not work in the 2024 edition
(in the `futures-core` dependency)
warning: `default_features` is deprecated in favor of `default-features` and will not work in the 2024 edition
(in the `futures-sink` dependency)

This does not cause the process to exit with a non-zero exit code, which means this would not have been effecting CI.

This PR fixes that warning.