doc: replace dead link in v8 module

Identified a dead link to the V8 GetHeapSpaceStatistics() function on the v8 module documentation page. I updated the link to the version from the 6.10 version of the V8 docs, but could easily update it to the 8.0 version if desired, for some reason.

Checklist

• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc