DOCSP-20036 fix indents (#135)

Author: Dave

source/reference/operator/update/unset.txt

@@ -72,8 +72,9 @@ value of ``sku`` is ``unknown``:
    )
 
 :method:`~db.collection.updateOne()` uses the :update:`$unset` operator to:
-   - remove the ``quantity`` field
-   - remove the ``instock`` field
+
+- remove the ``quantity`` field
+- remove the ``instock`` field
 
 .. code-block:: javascript
    :copyable: false