build(deps): bump convert from 3.0.2 to 3.1.1 (#155)

Bumps [convert](https://github.com/dart-lang/convert) from 3.0.2 to 3.1.1.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/dart-lang/convert/blob/master/CHANGELOG.md">convert's changelog</a>.</em></p>
<blockquote>
<h2>3.1.1</h2>
<ul>
<li>Require Dart 2.18</li>
<li>Fix a number of comment references.</li>
</ul>
<h2>3.1.0</h2>
<ul>
<li>Add a fixed-pattern DateTime formatter. See
<a href="https://github-redirect.dependabot.com/dart-lang/intl/issues/210">#210</a> in package:intl.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a href="https://github.com/dart-lang/convert/commits/v3.1.1">compare view</a></li>
</ul>
</details>
<br />


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</details>

pubspec.lock

@@ -49,7 +49,7 @@ packages:
       name: bech32
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.1"
+    version: "0.2.2"
   bip39:
     dependency: "direct main"
     description:
@@ -154,7 +154,7 @@ packages:
       name: convert
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.0.2"
+    version: "3.1.1"
   coverage:
     dependency: transitive
     description: