chore(deps): update dependency reactiveui.wpf to v20 (#89)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/ReactiveMvvm.Wpf/ReactiveMvvm.Wpf.csproj

@@ -6,7 +6,7 @@
     <UseWpf>true</UseWpf>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="ReactiveUI.WPF" Version="19.6.12" />
+    <PackageReference Include="ReactiveUI.WPF" Version="20.0.1" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\ReactiveMvvm\ReactiveMvvm.csproj" />