Invalid url for Breadth First Traversal in README.md

[R4j4t-Singh]

This issue is about invalid url (https://www.cs.bu.edu/teaching/c/tree/breadth-first/) for Breadth First Traversal in README.md .

• [x] Issue Title is in form Invalid url for Breadth First Traversal in README.md.
• [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• [x] This Algo/DS is worth adding to this repository.
• [x] Assign this issue to me (I want to work on this).
  • [x] I ensure that I am not already assigned to 2 or more issues.
• [x] I will send my PR only after I'm assigned to this issue by any maintainer.
• [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

[R4j4t-Singh]

@iiitv/algo-maintainers I want to work on this issue

[vidit2512]

GFI 👍.