Bump MaterialDesignThemes from 4.9.0 to 5.1.0

Bumps [MaterialDesignThemes](https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit) from 4.9.0 to 5.1.0.
- [Release notes](https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/releases)
- [Commits](MaterialDesignInXAML/MaterialDesignInXamlToolkit@v4.9.0...v5.1.0)

---
updated-dependencies:
- dependency-name: MaterialDesignThemes
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Shadowsocks.WPF/Shadowsocks.WPF.csproj

@@ -49,7 +49,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="MaterialDesignThemes" Version="4.9.0" />
+    <PackageReference Include="MaterialDesignThemes" Version="5.1.0" />
     <PackageReference Include="MdXaml" Version="1.21.0" />
     <PackageReference Include="OxyPlot.Wpf" Version="2.2.0" />
     <PackageReference Include="ReactiveUI.Events.WPF" Version="15.1.1" />