Made id final

-Mario Fernandez
-Àlex Codina

src/main/java/cat/udl/eps/softarch/demo/domain/Adoption.java

@@ -3,7 +3,7 @@
 import java.util.Date;
 
 public class Adoption extends UriEntity<Long> {
-    private Long id;
+    private final Long id;
     private String type;
     private Boolean confirmed;
     private Date startDate;