doc: fix typo e.g., => e.g.

Fixes: https://github.com/nodejs/code-and-learn/issues/58
PR-URL: https://github.com/nodejs/node/pull/9563
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Shigeki Ohtsu <ohtsu@ohtsu.org>

doc/api/dns.md

@@ -256,7 +256,7 @@ added: v0.1.90
 Uses the DNS protocol to resolve name server records (`NS` records) for the
 `hostname`. The `addresses` argument passed to the `callback` function will
 contain an array of name server records available for `hostname`
-(e.g., `['ns1.example.com', 'ns2.example.com']`).
+(e.g. `['ns1.example.com', 'ns2.example.com']`).
 
 ## dns.resolveSoa(hostname, callback)
 <!-- YAML