Bump syn from 1.0.107 to 1.0.108 (#2616)

Bumps [syn](https://github.com/dtolnay/syn) from 1.0.107 to 1.0.108.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/dtolnay/syn/releases">syn's releases</a>.</em></p>
<blockquote>
<h2>1.0.108</h2>
<ul>
<li>Fix handling of unusual whitespace after escaped newlines in <code>LitStr::value</code> (<a href="https://github-redirect.dependabot.com/dtolnay/syn/issues/1381">#1381</a>, thanks <a href="https://github.com/ModProg"><code>@​ModProg</code></a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/dtolnay/syn/commit/01f69e937c7d389b01edb0ff3bd8b1c42c73824c"><code>01f69e9</code></a> Release 1.0.108</li>
<li><a href="https://github.com/dtolnay/syn/commit/62d0aeda487a835a3a28d5efeb24b92c68ab3834"><code>62d0aed</code></a> stricter parsing of string_continue escapes</li>
<li>See full diff in <a href="https://github.com/dtolnay/syn/compare/1.0.107...1.0.108">compare view</a></li>
</ul>
</details>
<br />


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</details>

boa_macros/Cargo.toml

@@ -14,6 +14,6 @@ proc-macro = true
 
 [dependencies]
 quote = "1.0.23"
-syn = "1.0.107"
+syn = "1.0.108"
 proc-macro2 = "1.0"
 synstructure = "0.12"