SQL: [Docs] Fix typo

Add missing closing "`".

Follows: 78a1185

Author: matriv

docs/reference/sql/limitations.asciidoc

@@ -118,7 +118,7 @@ SELECT * FROM test GROUP BY age ORDER BY COUNT(*) LIMIT 100;
 It is possible to run the same queries without a `LIMIT` however in that case if the maximum size (*10000*) is passed,
 an exception will be returned as {es-sql} is unable to track (and sort) all the results returned.
 
-Moreover, the aggregation(s) used in the `ORDER BY must be only plain aggregate functions. No scalar
+Moreover, the aggregation(s) used in the `ORDER BY` must be only plain aggregate functions. No scalar
 functions or operators can be used, and therefore no complex columns that combine two ore more aggregate
 functions can be used for ordering. Here are some examples of queries that are *not allowed*: