doc: util.isDeepStrictEqual returns boolean

PR-URL: nodejs/node#16653
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>

Author: azz

doc/api/util.md

@@ -462,7 +462,7 @@ added: REPLACEME
 
 * `val1` {any}
 * `val2` {any}
-* Returns: {string}
+* Returns: {boolean}
 
 Returns `true` if there is deep strict equality between `val` and `val2`.
 Otherwise, returns `false`.