merge: #20

20: Bump regex from 1.5.4 to 1.5.6 r=fnichol a=dependabot[bot]

Bumps [regex](https://github.com/rust-lang/regex) from 1.5.4 to 1.5.6.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/rust-lang/regex/blob/master/CHANGELOG.md">regex's changelog</a>.</em></p>
<blockquote>
<h1>1.5.6 (2022-05-20)</h1>
<p>This release includes a few bug fixes, including a bug that produced incorrect
matches when a non-greedy <code>?</code> operator was used.</p>
<ul>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/680">#680</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/680">rust-lang/regex#680</a>):
Fixes a bug where <code>[[:alnum:][:^ascii:]]</code> dropped <code>[:alnum:]</code> from the class.</li>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/859">#859</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/859">rust-lang/regex#859</a>):
Fixes a bug where <code>Hir::is_match_empty</code> returned <code>false</code> for <code>\b</code>.</li>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/862">#862</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/862">rust-lang/regex#862</a>):
Fixes a bug where 'ab??' matches 'ab' instead of 'a' in 'ab'.</li>
</ul>
<h1>1.5.5 (2022-03-08)</h1>
<p>This releases fixes a security bug in the regex compiler. This bug permits a
vector for a denial-of-service attack in cases where the regex being compiled
is untrusted. There are no known problems where the regex is itself trusted,
including in cases of untrusted haystacks.</p>
<ul>
<li><a href="https://github.com/rust-lang/regex/security/advisories/GHSA-m5pq-gvj9-9vr8">SECURITY #GHSA-m5pq-gvj9-9vr8</a>:
Fixes a bug in the regex compiler where empty sub-expressions subverted the
existing mitigations in place to enforce a size limit on compiled regexes.
The Rust Security Response WG published an advisory about this:
<a href="https://groups.google.com/g/rustlang-security-announcements/c/NcNNL1Jq7Yw">https://groups.google.com/g/rustlang-security-announcements/c/NcNNL1Jq7Yw</a></li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/rust-lang/regex/commit/9aef5b1edc2a436244b936db53a03ed6d720e87e"><code>9aef5b1</code></a> 1.5.6</li>
<li><a href="https://github.com/rust-lang/regex/commit/2931b070fd9b525dec95c2b4c91f8b9ee500239e"><code>2931b07</code></a> syntax: bump minimum regex-syntax version to 0.6.26</li>
<li><a href="https://github.com/rust-lang/regex/commit/b41bde0b854e3cd1018f55e5dcd80c09b418d6c4"><code>b41bde0</code></a> regex-syntax-0.6.26</li>
<li><a href="https://github.com/rust-lang/regex/commit/d98da65bb3df16836f1181c6f7e4f03c3af1d5a5"><code>d98da65</code></a> changelog: 1.5.6</li>
<li><a href="https://github.com/rust-lang/regex/commit/1c19619672c2ef16dc9f64fec38af5719c4ec06c"><code>1c19619</code></a> syntax: fix literal extraction for 'ab??'</li>
<li><a href="https://github.com/rust-lang/regex/commit/88a2a62d861d189faae539990f63cb9cf195bd8c"><code>88a2a62</code></a> syntax: fix 'is_match_empty' predicate</li>
<li><a href="https://github.com/rust-lang/regex/commit/72f09f1aeb0ff3f703b1afdbdd21f5ff63162fb4"><code>72f09f1</code></a> syntax: fix ascii class union bug</li>
<li><a href="https://github.com/rust-lang/regex/commit/b5372864e2df6a2f5e543a556a62197f50ca3650"><code>b537286</code></a> doc: fix some typos</li>
<li><a href="https://github.com/rust-lang/regex/commit/258bdf798a14f50529c1665e84cc8a3a9e2c90fc"><code>258bdf7</code></a> changelog: 1.5.5</li>
<li><a href="https://github.com/rust-lang/regex/commit/d130381b150756ba7e5940efdc6ebdf47f4febc0"><code>d130381</code></a> 1.5.5</li>
<li>Additional commits viewable in <a href="https://github.com/rust-lang/regex/compare/1.5.4...1.5.6">compare view</a></li>
</ul>
</details>
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