Update doc/api/worker_threads.md

Oh how I so dislike apostrophes

Co-authored-by: Anna Henningsen <anna@addaleax.net>

doc/api/worker_threads.md

@@ -71,7 +71,7 @@ added: REPLACEME
 Within a worker thread, `worker.environmentData` is a {Map} containing a clone
 of data passed to the spawning thread's `worker.setEnvironmentData()` function.
 The `worker.environmentData` is similar to `worker.workerData` except that
-every new `Worker` receives it's own copy of `worker.environmentData`
+every new `Worker` receives its own copy of `worker.environmentData`
 automatically.
 
 ```js