Fix description diff in activity (#4283)

Signed-off-by: Kristina Fefelova <kristin.fefelova@gmail.com>

models/view/src/index.ts

@@ -477,7 +477,15 @@ export function createModel (builder: Builder): void {
     editor: view.component.HTMLEditor
   })
 
-  classPresenter(builder, core.class.TypeCollaborativeMarkup, view.component.MarkupPresenter)
+  classPresenter(
+    builder,
+    core.class.TypeCollaborativeMarkup,
+    view.component.MarkupPresenter,
+    undefined,
+    undefined,
+    view.component.MarkupDiffPresenter
+  )
+
   builder.mixin(core.class.TypeCollaborativeMarkup, core.class.Class, view.mixin.InlineAttributEditor, {
     editor: view.component.CollaborativeHTMLEditor
   })