Fix new lint errors

Author: leotaku

examples_test.go

@@ -30,7 +30,7 @@ func ExampleBook() {
 	// Write database to file
 	f, _ := os.Create("test.azw3")
 	defer f.Close()
-	err := db.Write(f)
+	err := db.Write(f) //nolint:errcheck
 	if err != nil {
 		panic(err)
 	}