MDNJS: Update URI namespace

Mozilla apparently changed their namespace by adding a `Web` sub-segment.  They redirected from the previous namespace correctly, but (1) it was annoying and (2) the `fetch`/`parse` scripts wouldn't download/index any new updates.

I did:

- Review the recent Mozilla site map,
- Determine that all relevant entries have indeed been moved to `Web/` (can somebody confirm?)
- Modify the `fetch.sh` script to correct the pattern.
- Run `fetch.sh` and `parse.sh` to generate a new `output.txt` (could somebody review it or regenerate it?)