Update tokio requirement from 0.1.22 to 0.2.11

[dependabot-preview]

Updates the requirements on tokio to permit the latest version.

Release notes

Sourced from tokio's releases.

Tokio v0.2.11

Introduces select!, join!, and try_join! macros for waiting on multiple async operations concurrently from the same task. These macros are implemented primarily as declarative macros, which works around the recursion limit issue. The select! macro works with any type that implements Future and does not require special FusedFuture traits.

Fixes

• docs: misc fixes and tweaks (#2155, #2103, #2027, #2167, #2175).
• macros: handle generics in #[tokio::main] method (#2177).
• sync: broadcast potential lost notifications (#2135).
• rt: improve "no runtime" panic messages (#2145).

Added

• optional support for using parking_lot internally (#2164).
• fs: fs::copy, an async version of std::fs::copy (#2079).
• macros: select! waits for the first branch to complete (#2152).
• macros: join! waits for all branches to complete (#2158).
• macros: try_join! waits for all branches to complete or the first error (#2169).
• macros: pin! pins a value to the stack (#2163).
• net: ReadHalf::poll() and ReadHalf::poll_peak (#2151)
• stream: StreamExt::timeout() sets a per-item max duration (#2149).
• stream: StreamExt::fold() applies a function, producing a single value. (#2122).
• sync: impl Eq, PartialEq for oneshot::RecvError (#2168).
• task: methods for inspecting the JoinError cause (#2051).

Commits

• 00e3c29 chore: prepare v0.2.11 release (#2179)
• bcba4aa docs: write sync mod API docs (#2175)
• 71c47fa chore: bump nightly version used in CI (#2178)
• 4996e27 macros: fix skipping generics on #[tokio::main] (#2177)
• 5bf06f2 future: provide try_join! macro (#2169)
• 12be90e stream: add StreamExt::timeout() (#2149)
• 0d49e11 sync: impl equality traits for oneshot::RecvError (#2168)
• 9eca96a rt: improve "no runtime" panic messages (#2145)
• a16c9a5 rt: test block_in_place followed by Pending (#2120)
• f0bfebb fs: add fs::copy (#2079)
• Additional commits viewable in compare view

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[ebkalderon]

Blocked on #58.

[dependabot-preview]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.