Tweak link tag in module 5 doc

Author: DamianEdwards

docs/5. Add personal agenda.md

@@ -381,7 +381,7 @@ In this section we'll add features that track attendees who have registered on t
 1. The above markup uses a star icon from the [ionicons](https://ionicons.com/), one of the [icon libraries recommended by Bootstrap](https://getbootstrap.com/docs/4.0/extend/icons/). Let's add a CDN reference to this library in `Pages\Shared\_Layout.cshtml`, directly above the `site.css` reference:
     ``` html
     </environment>
-    <link href="https://unpkg.com/[email protected]/dist/css/ionicons.min.css" rel="stylesheet">
+    <link rel="stylesheet" href="https://unpkg.com/[email protected]/dist/css/ionicons.min.css" />
     <link rel="stylesheet" href="~/css/site.css" />
     ```
 1. Add `OnPostAsync` handlers to `Session.cshtml.cs` that handles the adding/removing of the session to the personal agenda: