doc: change worker.takeHeapSnapshot to getHeapSnapshot

Adapt doc to match implementation which exports getHeapSnapshot().

Author: Flarna

doc/api/worker_threads.md

@@ -685,7 +685,7 @@ inside the worker thread. If `stdout: true` was not passed to the
 [`Worker`][] constructor, then data will be piped to the parent thread's
 [`process.stdout`][] stream.
 
-### `worker.takeHeapSnapshot()`
+### `worker.getHeapSnapshot()`
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