Auto merge of #28518 - servo:dependabot/cargo/rand-0.7.3, r=jdm

Bump rand from 0.7.2 to 0.7.3

Bumps [rand](https://github.com/rust-random/rand) from 0.7.2 to 0.7.3.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/rust-random/rand/blob/master/CHANGELOG.md">rand's changelog</a>.</em></p>
<blockquote>
<h2>[0.7.3] - 2020-01-10</h2>
<h3>Fixes</h3>
<ul>
<li>The <code>Bernoulli</code> distribution constructors now reports an error on NaN and on
<code>denominator == 0</code>. (<a href="https://github-redirect.dependabot.com/rust-random/rand/issues/925">#925</a>)</li>
<li>Use <code>std::sync::Once</code> to register fork handler, avoiding possible atomicity violation (<a href="https://github-redirect.dependabot.com/rust-random/rand/issues/928">#928</a>)</li>
<li>Fix documentation on the precision of generated floating-point values</li>
</ul>
<h3>Changes</h3>
<ul>
<li>Unix: make libc dependency optional; only use fork protection with std feature (<a href="https://github-redirect.dependabot.com/rust-random/rand/issues/928">#928</a>)</li>
</ul>
<h3>Additions</h3>
<ul>
<li>Implement <code>std::error::Error</code> for <code>BernoulliError</code> (<a href="https://github-redirect.dependabot.com/rust-random/rand/issues/919">#919</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="074cb6a997"><code>074cb6a</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/rust-random/rand/issues/929">#929</a> from dhardy/master</li>
<li><a href="0f4e152c1c"><code>0f4e152</code></a> Prepare rand 0.7.3 release</li>
<li><a href="5b0d874369"><code>5b0d874</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/rust-random/rand/issues/928">#928</a> from dhardy/libc</li>
<li><a href="ae4683cec7"><code>ae4683c</code></a> Remove use of deprecated ATOMIC_USIZE_INIT</li>
<li><a href="ae3a416ecc"><code>ae3a416</code></a> Fix <a href="https://github-redirect.dependabot.com/rust-random/rand/issues/911">#911</a>: use Once instead of AtomicBool</li>
<li><a href="a67173ef63"><code>a67173e</code></a> make libc dependency optional (fork protection requires std)</li>
<li><a href="e2dc2c3848"><code>e2dc2c3</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/rust-random/rand/issues/926">#926</a> from dhardy/fmt</li>
<li><a href="fab964d194"><code>fab964d</code></a> Manual function specification reformatting</li>
<li><a href="3a5d5a8e7a"><code>3a5d5a8</code></a> Use rustfmt::skip for some cases</li>
<li><a href="3a51c3e0e2"><code>3a51c3e</code></a> Manual array reformatting</li>
<li>Additional commits viewable in <a href="https://github.com/rust-random/rand/compare/0.7.2...0.7.3">compare view</a></li>
</ul>
</details>
<br />

[![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=rand&package-manager=cargo&previous-version=0.7.2&new-version=0.7.3)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores)

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

You can trigger Dependabot actions by commenting on this PR:
- `@dependabot rebase` will rebase this PR
- `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it
- `@dependabot merge` will merge this PR after your CI passes on it
- `@dependabot squash and merge` will squash and merge this PR after your CI passes on it
- `@dependabot cancel merge` will cancel a previously requested merge and block automerging
- `@dependabot reopen` will reopen this PR if it is closed
- `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
- `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
- `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
- `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

</details>

Cargo.lock

@@ -4825,9 +4825,9 @@ dependencies = [
 
 [[package]]
 name = "rand"
-version = "0.7.2"
+version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3ae1b169243eaf61759b8475a998f0a385e42042370f3a7dbaf35246eacc8412"
+checksum = "6a6b1679d49b24bbfe0c803429aa1874472f50d9b363131f0e89fc356b544d03"
 dependencies = [
  "getrandom",
  "libc",