Page 81, immutability

On page 81, the text after Output 2.14 says:

> If the immutability of a string is ignored, mistakes like those shown in Listing 2.17 can occur with other string methods as well.

Listing 2.17 is on page 70, eleven pages back. I think it should refer to Listing 2.23.

/rob

Review the text after Output 2.14 on page 81 and compare its reference with Listing 2.17 on page 70 and Listing 2.23. Update the listing reference so the passage points to Listing 2.23, then verify that the surrounding text and pagination remain correct.

Scritto dal modello di indicizzazione a partire dal testo della issue.