Autofocus delete tag button in when dialog opens (#2775)

This puts focus on the delete tag button when the dialog is opened and allows you to hit return/enter on the keyboard to confirm the deletion.

lib/dialogs/trash-tag-confirmation/index.tsx

@@ -34,6 +34,7 @@ const TrashTagConfirmation: FunctionComponent<Props> = ({
     </div>
     <div className="dialog-buttons">
       <button
+        autoFocus
         className="button-primary delete-tag"
         onClick={() => trashTag(tagName)}
       >