* Upgrade futures, async-stream, and futures_codec
These were the last three dependencies on futures-preview. `nu` itself
is now fully dependent on `futures@0.3`, as opposed to `futures-preview`
alpha.
Because the update to `futures` from `0.3.0-alpha.19` to `0.3.0` removed
the `Stream` implementation of `VecDeque` ([changelog][changelog]), most
commands that convert a `VecDeque` to an `OutputStream` broke and had to
be fixed.
The current solution is to now convert `VecDeque`s to a `Stream` via
`futures::stream::iter`. However, it may be useful for `futures` to
create an `IntoStream` trait, implemented on the `std::collections` (or
really any `IntoIterator`). If something like this happends, it may be
worthwhile to update the trait implementations on `OutputStream` and
refactor these commands again.
While upgrading `futures_codec`, we remove a custom implementation of
`LinesCodec`, as one has been added to the library. There's also a small
refactor to make the stream output more idiomatic.
[changelog]: https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md#030---2019-11-5
* Upgrade sys & ps plugin dependencies
They were previously dependent on `futures-preview`, and `nu_plugin_ps`
was dependent on an old version of `futures-timer`.
* Remove dependency on futures-timer from nu
* Update Cargo.lock
* Fix formatting
* Revert fmt regressions
CI is still on 1.40.0, but the latest rustfmt v1.41.0 has changes to the
`val @ pattern` syntax, causing the linting job to fail.
* Fix clippy warnings
