bot (deps): bump reactiveui from 18.3.1 to 18.4.20 in /Cosmic.NET (#74)

Author: dependabot[bot]

cosmo/Cosmo.csproj

@@ -7,6 +7,6 @@
     <Copyright>Copyright © Joshua Kempner 2008-2022</Copyright>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="reactiveui" Version="18.3.1" />
+    <PackageReference Include="reactiveui" Version="18.4.20" />
   </ItemGroup>
 </Project>