fix(collections): 🐛 calculations, ajustes no texto

Author: rcmoutinho

book/08-java-collections/sections/04-calculations.asc

@@ -82,6 +82,7 @@ include::{section-java-package}/calculations/Collections_PartitioningBy.java[tag
 Mapa de pares e ímpares: {false=[1, 3, 5, 7, 9], true=[2, 4, 6, 8]}
 ----
 
+.Referências
 ****
 
 * Using Streams
@@ -90,4 +91,4 @@ Boyarsky, Jeanne; Selikoff, Scott. OCP: Oracle Certified Professional Java SE 8
 
 * https://www.baeldung.com/java-8-streams[The Java 8 Stream API Tutorial.]
 
-****
+****