Chapter 12 in table of contents leads to 404

[michal880]

• Steps to reproduce:
  go to README.md, navigate to table of contents, click chapter 12

• Unexpcted behaviour:
  link leads to 404 on https://github.com/alexeyzimarev/ddd-book/tree/master/chapter12

[alexeyzimarev]

Closed in f2edec9