Auto merge of #26914 - servo:dependabot/cargo/futures-util-0.3.5, r=jdm

build(deps): bump futures-util from 0.3.4 to 0.3.5

Bumps [futures-util](https://github.com/rust-lang/futures-rs) from 0.3.4 to 0.3.5.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/rust-lang/futures-rs/releases">futures-util's releases</a>.</em></p>
<blockquote>
<h2>0.3.5</h2>
<ul>
<li>Added <code>StreamExt::flat_map</code>.</li>
<li>Added <code>StreamExt::ready_chunks</code>.</li>
<li>Added <code>*_unpin</code> methods to <code>SinkExt</code>.</li>
<li>Added a <code>cancellation()</code> future to <code>oneshot::Sender</code>.</li>
<li>Added <code>reunite</code> method to <code>ReadHalf</code> and <code>WriteHalf</code>.</li>
<li>Added <code>Extend</code> implementations for <code>Futures(Un)Ordered</code> and <code>SelectAll</code>.</li>
<li>Added support for reexporting the <code>join!</code> and <code>select!</code> macros.</li>
<li>Added <code>no_std</code> support for the <code>pending!</code> and <code>poll!</code> macros.</li>
<li>Added <code>Send</code> and <code>Sync</code> support for <code>AssertUnmoved</code>.</li>
<li>Fixed a bug where <code>Shared</code> wasn't relinquishing control to the executor.</li>
<li>Removed the <code>Send</code> bound on the output of <code>RemoteHandle</code>.</li>
<li>Relaxed bounds on <code>FuturesUnordered</code>.</li>
<li>Reorganized internal tests to work under different <code>--feature</code>s.</li>
<li>Reorganized the bounds on <code>StreamExt::forward</code>.</li>
<li>Removed and replaced a large amount of internal <code>unsafe</code>.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md">futures-util's changelog</a>.</em></p>
<blockquote>
<h1>0.3.5 - 2020-05-08</h1>
<ul>
<li>Added <code>StreamExt::flat_map</code>.</li>
<li>Added <code>StreamExt::ready_chunks</code>.</li>
<li>Added <code>*_unpin</code> methods to <code>SinkExt</code>.</li>
<li>Added a <code>cancellation()</code> future to <code>oneshot::Sender</code>.</li>
<li>Added <code>reunite</code> method to <code>ReadHalf</code> and <code>WriteHalf</code>.</li>
<li>Added <code>Extend</code> implementations for <code>Futures(Un)Ordered</code> and <code>SelectAll</code>.</li>
<li>Added support for reexporting the <code>join!</code> and <code>select!</code> macros.</li>
<li>Added <code>no_std</code> support for the <code>pending!</code> and <code>poll!</code> macros.</li>
<li>Added <code>Send</code> and <code>Sync</code> support for <code>AssertUnmoved</code>.</li>
<li>Fixed a bug where <code>Shared</code> wasn't relinquishing control to the executor.</li>
<li>Removed the <code>Send</code> bound on the output of <code>RemoteHandle</code>.</li>
<li>Relaxed bounds on <code>FuturesUnordered</code>.</li>
<li>Reorganized internal tests to work under different <code>--feature</code>s.</li>
<li>Reorganized the bounds on <code>StreamExt::forward</code>.</li>
<li>Removed and replaced a large amount of internal <code>unsafe</code>.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/rust-lang/futures-rs/commit/4ceafb384c18e664a507892b16c98322a6e240a1"><code>4ceafb3</code></a> Stage 0.3.5</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/5b91728e10a47742d3913501fc13ff0da240bdd5"><code>5b91728</code></a> Drop unneeded Send/Sync bound from AssertUnmoved</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/4b930bb4702b1f57cabe3ae6d9c499833bd7d520"><code>4b930bb</code></a> Implement Send + Sync for AssertUnmoved</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/3bf5ac99e939e6ff70283937fa91e8d77e5f70e8"><code>3bf5ac9</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/rust-lang/futures-rs/issues/2128">#2128</a> from Diggsey/snip</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/1b44548be753ff0b7d2e4eabe7de4d2e199cfaf2"><code>1b44548</code></a> Merge branch 'master' into snip</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/32005e3f74f2b48a9ca0e97a63ff25976c863703"><code>32005e3</code></a> fix: Shared must relinquish control to the executor if repolled</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/dc06edaf5428009fb4189af5a64cc2d23bd3955c"><code>dc06eda</code></a> Update pin-utils to 0.1</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/dc00793b38acfb5cf001ad975b60bb94ef0d45ae"><code>dc00793</code></a> Make ready and lazy's panic messages easy to understand</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/127b244ecd779b4be0e59218986c2b3708f862f9"><code>127b244</code></a> Allow pending! and poll! in no_std</li>
<li><a href="https://github.com/rust-lang/futures-rs/commit/dfc66739469a4fe849987a676c9b3be6011f1fb8"><code>dfc6673</code></a> Update futures-util/src/future/future/flatten.rs</li>
<li>Additional commits viewable in <a href="https://github.com/rust-lang/futures-rs/compare/0.3.4...0.3.5">compare view</a></li>
</ul>
</details>
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