doc: replace dead link in v8 module

PR-URL: #14372
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: drboyer

doc/api/v8.md

@@ -122,4 +122,4 @@ setTimeout(function() { v8.setFlagsFromString('--notrace_gc'); }, 60e3);
 
 [V8]: https://developers.google.com/v8/
 [here]: https://github.com/thlorenz/v8-flags/blob/master/flags-0.11.md
-[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-5.0/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4
+[`GetHeapSpaceStatistics`]: https://v8docs.nodesource.com/node-8.0/d5/dda/classv8_1_1_isolate.html#ac673576f24fdc7a33378f8f57e1d13a4