Update mio requirement from 0.6 to 0.7

[dependabot-preview]

Updates the requirements on mio to permit the latest version.

Release notes

Sourced from mio's releases.

Mio v0.7

Version 0.7 of Mio contains various major changes compared to version 0.6. Overall a large number of API changes have been made to reduce the complexity of the implementation and remove overhead where possible.

See the change log for details.

Changelog

Sourced from mio's changelog.

0.7.0

Version 0.7 of Mio contains various major changes compared to version 0.6. Overall a large number of API changes have been made to reduce the complexity of the implementation and remove overhead where possible.

Please refer to the blog post about 0.7-alpha.1 for additional information.

Added

• Interest structure that replaces Ready in registering event sources.
• Registry structure that separates the registering and polling functionality.
• Waker structure that allows another thread to wake a thread polling Poll.
• Unix Domain Socket (UDS) types: UnixDatagram, UnixListener and UnixStream.

Removed

• All code deprecated in 0.6 was removed in 0.7.
• Support for Fuchsia was removed as the code was unmaintained.
• Support for Bitrig was removed, rustc dropped support for it also.
• UnixReady was merged into Ready.
• Custom user-space readiness queue was removed, this includes the public Registration and SetReadiness types.
• PollOpt was removed and all registrations use edge-triggers. See the upgrade guide on how to process event using edge-triggers.
• The network types (types in the net module) now support only the same API as found in the standard library, various methods on the types were removed.
• TcpStream now supports vectored I/O.
• Poll::poll_interruptible was removed. Instead Poll::poll will now return an error if one occurs.
• From<usize> is removed from Token, the internal field is still public, so Token(my_token) can still be used.

Changed

• Various documentation improvements were made around correct usage of Poll and registered event sources. It is recommended to reread the documentation of at least event::Source and Poll.
• Mio now uses Rust 2018 and rustfmt for all code.
• Event was changed to be a wrapper around the OS event. This means it can be significantly larger on some OSes.
• Ready was removed and replaced with various is_* methods on Event. For example instead checking for readable readiness using Event::ready().is_readble(), you would call Event::is_readble().
• Ready::is_hup was removed in favour of Event::is_read_closed and Event::is_write_closed.
• The Iterator implementation of Events was changed to return &Event.

... (truncated)

Commits

• 5da8c49 Release v0.7.0
• db87265 Remove outdated comment from Poll::poll
• ad56f9c Update changelog to reflect all changes in 0.7 (#1278)
• a4f1151 Don't ignore errors in Windows selector (#1277)
• 9bbba42 Expand on documentation (#1264)
• 10df3e1 A partial fix for issue #1191. Do not panic mio on sockstate error, instead k...
• 653b6cf Accept IPv4 multicast addresses by reference
• 0f4003d Add comments on how to run the examples
• 9ac8bc7 Make Events' fmt::Debug implementation more useful
• d394e2f Improve changelog wording
• Additional commits viewable in compare view

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