doc: add change info for async_hooks.executionAsyncId()

Add meta information to async_hooks documentation informing that executionAsyncId was renamed from currentId at Node.js 8.2.0.

Not sure if maybe it'd be more correct to show it as "added" rather than "changed" at 8.2.0. Thoughts, @nodejs/documentation ?

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc