doc: fix dns.resolveCname description typo

PR-URL: #5622
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/dns.markdown

@@ -181,7 +181,7 @@ will contain an array of IPv6 addresses.
 
 Uses the DNS protocol to resolve `CNAME` records for the `hostname`. The
 `addresses` argument passed to the `callback` function
-will contain an of canonical name records available for the `hostname`
+will contain an array of canonical name records available for the `hostname`
 (e.g. `['bar.example.com']`).
 
 ## dns.resolveMx(hostname, callback)