WebSocketApp: stop using floating numbers

Otherwise when starting to use nuget Centralized Package
Management we would get this error:

```
error NU1011: Centrally defined floating package versions are not allowed.
```

src/WebSocketApp/WebSocketApp.fsproj

@@ -23,9 +23,9 @@
     <Compile Include="Middleware\WebSocketMiddleware.fs" />
     <Compile Include="Program.fs" />
     <None Include="web.config" CopyToOutputDirectory="PreserveNewest" />
-    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.*" />
+    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.34" />
     <PackageReference Include="Giraffe" Version="3.1.0" />
-    <PackageReference Include="Giraffe.Razor" Version="1.3.*" />
+    <PackageReference Include="Giraffe.Razor" Version="1.3.0" />
     <Watch Include="**\*.cshtml" Exclude="bin\**\*" />
     <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.1.1" />
     <PackageReference Include="TaskBuilder.fs" Version="2.1.0" />