FIX: Reorder categories not working

Ember was throwing this error preventing the reorder categories feature
from working:

```
access theidproperty (of <(unknown):ember1803>). ... the object in question
is a special kind of Ember object (a proxy). Therefore, it is still necessary
to use.get('id')in this case.
```

So I updated it to use the `get` method

https://api.emberjs.com/ember/3.14/functions/@ember%2Fobject/get

Follow up to: 6e5fedb312

app/assets/javascripts/discourse/helpers/category-link.js.es6

@@ -79,7 +79,9 @@ function defaultCategoryLinkRenderer(category, opts) {
   let restricted = get(category, "read_restricted");
   let url = opts.url
     ? opts.url
-    : Discourse.getURL(`/c/${Category.slugFor(category)}/${category.id}`);
+    : Discourse.getURL(
+        `/c/${Category.slugFor(category)}/${get(category, "id")}`
+      );
   let href = opts.link === false ? "" : url;
   let tagName = opts.link === false || opts.link === "false" ? "span" : "a";
   let extraClasses = opts.extraClasses ? " " + opts.extraClasses : "";