doc: dns.resolve fix callback argument description

The dns.resolve documentation stated that an array of IP
addresses would be returned in the callback. This is true
for everything other than the SOA record which returns an object.
This fixes that documentation.

Fixes: https://github.com/nodejs/node/issues/6506
PR-URL: https://github.com/nodejs/node/pull/7532
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Roman Reiss <me@silverwind.io>

doc/api/dns.md

@@ -158,7 +158,9 @@ Valid values for `rrtype` are:
  * `'NAPTR'` - name authority pointer record
 
 The `callback` function has arguments `(err, addresses)`. When successful,
-`addresses` will be an array. The type of each  item in `addresses` is
+`addresses` will be an array, except when resolving an SOA record which returns
+an object structured in the same manner as one returned by the
+[`dns.resolveSoa()`][] method. The type of each item in `addresses` is
 determined by the record type, and described in the documentation for the
 corresponding lookup methods.
 
@@ -379,6 +381,7 @@ uses. For instance, _they do not use the configuration from `/etc/hosts`_.
 [`dns.lookup()`]: #dns_dns_lookup_hostname_options_callback
 [`dns.resolve()`]: #dns_dns_resolve_hostname_rrtype_callback
 [`dns.resolve4()`]: #dns_dns_resolve4_hostname_callback
+[`dns.resolveSoa()`]: #dns_dns_resolvesoa_hostname_callback
 [`Error`]: errors.html#errors_class_error
 [Implementation considerations section]: #dns_implementation_considerations
 [supported `getaddrinfo` flags]: #dns_supported_getaddrinfo_flags