Auto merge of #13416 - vigneshsarma:issue-13408, r=jdm

Replace instances of old ServiceWorker specification URL with new one

<!-- Please describe your changes on the following line: -->

The old specification URL is
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/, which has
been replaced by the new one at https://w3c.github.io/ServiceWorker/.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #13408 (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because all the changes are in commented parts of the code.

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

The old specification URL is
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/ has
been replaced by the new one at https://w3c.github.io/ServiceWorker/.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13416)
<!-- Reviewable:end -->

0 files changed, 0 insertions, 0 deletions