build(deps): update ReactiveUI.AndroidSupport requirement in /src (#332)

Updates the requirements on [ReactiveUI.AndroidSupport](https://github.com/reactiveui/reactiveui) to permit the latest version.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@14.1.1...15.1.1)

---
updated-dependencies:
- dependency-name: ReactiveUI.AndroidSupport
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/ReactiveUI.Validation.AndroidSupport/ReactiveUI.Validation.AndroidSupport.csproj

@@ -11,7 +11,7 @@
 
   <ItemGroup>
     <PackageReference Include="Xamarin.Android.Support.Design" Version="28.*" />
-    <PackageReference Include="ReactiveUI.AndroidSupport" Version="14.*" />
+    <PackageReference Include="ReactiveUI.AndroidSupport" Version="15.*" />
   </ItemGroup>
 
   <ItemGroup>