fix: invalid sorting of table of contents; #91

Issue: https://github.com/ochococo/Design-Patterns-In-Swift/issues/121 - [x] Read [CONTRIBUTING.md]](https://github.com/ochococo/Design-Patterns-In-Swift/blob/master/CONTRIBUTING.md]) - [x] Added description - [x] Linked to and/or created issue ### 📖 Description This PR fixes the issue with the invalid sorting in Table of Contents in `README.md`. In `Behavioral` section, the `Visitor` pattern should be after `Template Method` pattern. ### 📷 Screenshot <img width="604" alt="Screenshot 2023-06-29 at 21 56 45" src="https://github.com/ochococo/Design-Patterns-In-Swift/assets/2694531/d38b8e27-df4e-44de-973d-365ce664c24e">