Auto merge of #26399 - utsavoza:ugo/doc-fixes/03-05-2020, r=jdm
Auto merge of #26399 - utsavoza:ugo/doc-fixes/03-05-2020, r=jdm

Update doc links and code snippet for trace implementation in JS-Servos-only-GC.md

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes update the outdated doc links and code snippet for trace implementation.
- [x] These changes do not require tests because these are doc fixes.

splav/servo,splav/servo,splav/servo,KiChjang/servo,KiChjang/servo,KiChjang/servo,KiChjang/servo,KiChjang/servo,splav/servo,KiChjang/servo,KiChjang/servo,splav/servo,splav/servo,KiChjang/servo,splav/servo,splav/servo,KiChjang/servo,splav/servo,splav/servo,KiChjang/servo