Docs: fold section into current chapter
In we added a new *chapter* on aggregating by day of the
week. We intended to add a new *section* but we were missing a
single `=`.
@@ -398,7 +398,7 @@ the `order` setting. Supports the same `order` functionality as the <<search-agg
deprecated[6.0.0, Use `_key` instead of `_time` to order buckets by their dates/keys]
-=== Use of a script to aggregate by day of the week
+==== Use of a script to aggregate by day of the week
There are some cases where date histogram can't help us, like for example, when we need
to aggregate the results by day of the week.
