Updated Host to use .NET 5

Currently, none of the core OnTopic libraries rely on .NET 5 specific capabilities and, therefore, none of them multi-target .NET 5. That said, we _expect_ most implementors to be using .NET 5 and, therefore, it makes sense that the host example will be running in .NET 5 itself. That should also provide it with some performance benefits.

Author: JeremyCaney

OnTopic.AspNetCore.Mvc.Host/OnTopic.AspNetCore.Mvc.Host.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp3.1</TargetFrameworks>
-    <LangVersion>9.0</LangVersion>
+    <TargetFrameworks>net5.0</TargetFrameworks>
     <UserSecretsId>62eb85bf-f802-4afd-8bec-3d344e1cfc79</UserSecretsId>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
@@ -18,4 +17,4 @@
     <ProjectReference Include="..\OnTopic.All\OnTopic.All.csproj" />
   </ItemGroup>
 
-</Project>
+</Project>