Reformat Author and Book classes for online readability

Since this code is meant to be embedded in the guide itself, we should
introduce newlines to improve the page layout and avoid scrolls.

complete/src/main/java/com/example/graphqlserver/Author.java

@@ -12,6 +12,9 @@ public record Author (String id, String firstName, String lastName) {
     );
 
     public static Author getById(String id) {
-        return authors.stream().filter(author -> author.id().equals(id)).findFirst().orElse(null);
+        return authors.stream()
+				.filter(author -> author.id().equals(id))
+				.findFirst()
+				.orElse(null);
     }
 }

complete/src/main/java/com/example/graphqlserver/Book.java

@@ -12,6 +12,9 @@ public record Book (String id, String name, int pageCount, String authorId) {
     );
 
     public static Book getById(String id) {
-        return books.stream().filter(book -> book.id().equals(id)).findFirst().orElse(null);
+        return books.stream()
+				.filter(book -> book.id().equals(id))
+				.findFirst()
+				.orElse(null);
     }
 }