doc: clarify async/asynchronous in deprecations.md

Change _async_ to _asynchronous_ in `deprecations.md` to avoid confusion
with the `async` keyword. This has the additional minor benefit of being
more formal and less conversational prose.

PR-URL: #15172
Reviewed-By: Timothy Gu <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>

doc/api/deprecations.md

@@ -148,7 +148,7 @@ Type: Runtime
 explicitly via error event handlers set on the domain instead.
 
 <a id="DEP0013"></a>
-### DEP0013: fs async function without callback
+### DEP0013: fs asynchronous function without callback
 
 Type: Runtime