Update README.md

Resolved the Invalid Sorting Issue #121 - [ ] Read [CONTRIBUTING.md](https://github.com/ochococo/Design-Patterns-In-Swift/blob/master/CONTRIBUTING.md]) - [x] Only edited files inside `source` folder (IMPORTANT) and commited them with a meaningful message - [ ] Ran `generate-playground.sh`, no errors - [ ] Opened playground, it worked fine - [ ] Did not commit the changes caused by `generate-playground.sh` - [ ] Linked to and/or created issue - [ ] Added a description to PR