Fix formatting

Author: stefano-ottolenghi

modules/ROOT/pages/expressions/list-expressions.adoc

@@ -301,7 +301,7 @@ RETURN list[0] + [2] + list[1..] AS newList
 [[list-concatenation]]
 == List concatenation
 
-Cypher contains two list concatenation operators: `||` and `+`.
+Cypher contains two list concatenation operators: `||` and `\+`.
 `||` is xref:appendix/gql-conformance/index.adoc[GQL conformant], while `+` is not.
 
 .List concatenation using `||` and `+`