Auto merge of #26865 - servo:dependabot/cargo/regex-1.3.9, r=jdm

build(deps): bump regex from 1.3.7 to 1.3.9

Bumps [regex](https://github.com/rust-lang/regex) from 1.3.7 to 1.3.9.
<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>1.3.9 (2020-05-28)</h1>
<p>This release fixes a MSRV (Minimum Support Rust Version) regression in the
1.3.8 release. Namely, while 1.3.8 compiles on Rust 1.28, it actually does not
compile on other Rust versions, such as Rust 1.39.</p>
<p>Bug fixes:</p>
<ul>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/685">#685</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/685">rust-lang/regex#685</a>):
Remove use of <code>doc_comment</code> crate, which cannot be used before Rust 1.43.</li>
</ul>
<h1>1.3.8 (2020-05-28)</h1>
<p>This release contains a couple of important bug fixes driven
by better support for empty-subexpressions in regexes. For
example, regexes like <code>b|</code> are now allowed. Major thanks to
<a href="https://github.com/sliquister">@sliquister</a> for implementing support for this
in <a href="https://github-redirect.dependabot.com/rust-lang/regex/pull/677">#677</a>.</p>
<p>Bug fixes:</p>
<ul>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/523">#523</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/pull/523">rust-lang/regex#523</a>):
Add note to documentation that spaces can be escaped in <code>x</code> mode.</li>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/524">#524</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/524">rust-lang/regex#524</a>):
Add support for empty sub-expressions, including empty alternations.</li>
<li>[BUG <a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/659">#659</a>](<a href="https://github-redirect.dependabot.com/rust-lang/regex/issues/659">rust-lang/regex#659</a>):
Fix match bug caused by an empty sub-expression miscompilation.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="691606773f"><code>6916067</code></a> 1.3.9</li>
<li><a href="d7fbd158f7"><code>d7fbd15</code></a> tests: remove use of doc_comment crate</li>
<li><a href="e0053461a8"><code>e005346</code></a> 1.3.8</li>
<li><a href="60e949b779"><code>60e949b</code></a> deps: bump regex-syntax minimum version to 0.6.18</li>
<li><a href="95047166ac"><code>9504716</code></a> regex-syntax-0.6.18</li>
<li><a href="0e39314947"><code>0e39314</code></a> changelog: 1.3.8</li>
<li><a href="5180a97466"><code>5180a97</code></a> compile: support empty patterns better</li>
<li><a href="ed581f5a0f"><code>ed581f5</code></a> tests: add tests involving the Empty regex</li>
<li><a href="d50d31ba77"><code>d50d31b</code></a> hir: make is_alternation_literal say false on Empty</li>
<li><a href="0785926099"><code>0785926</code></a> tests: confirm that some counted repetitions are rejected</li>
<li>Additional commits viewable in <a href="https://github.com/rust-lang/regex/compare/regex-1.3.7...1.3.9">compare view</a></li>
</ul>
</details>
<br />

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Cargo.lock

@@ -4387,9 +4387,9 @@ checksum = "4e1b7878800220a76a08f32c057829511440f65528b63b940f2f2bc145d7ac68"
 
 [[package]]
 name = "regex"
-version = "1.3.7"
+version = "1.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a6020f034922e3194c711b82a627453881bc4682166cabb07134a10c26ba7692"
+checksum = "9c3780fcf44b193bc4d09f36d2a3c87b251da4a046c87795a0d35f4f927ad8e6"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -4399,9 +4399,9 @@ dependencies = [
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.17"
+version = "0.6.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7fe5bd57d1d7414c6b5ed48563a2c855d995ff777729dcd91c369ec7fea395ae"
+checksum = "26412eb97c6b088a6997e05f69403a802a92d520de2f8e63c2b65f9e0f47c4e8"
 
 [[package]]
 name = "remove_dir_all"