doc: fix typo about cluster doc, (eg. -> e.g.)

Fixes: nodejs/code-and-learn#58
PR-URL: #9568
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Shigeki Ohtsu <ohtsu@ohtsu.org>

Author: YutamaKotaro

doc/api/cluster.md

@@ -144,7 +144,7 @@ added: v0.11.2
 -->
 
 * `code` {Number} the exit code, if it exited normally.
-* `signal` {String} the name of the signal (eg. `'SIGHUP'`) that caused
+* `signal` {String} the name of the signal (e.g. `'SIGHUP'`) that caused
   the process to be killed.
 
 Similar to the `cluster.on('exit')` event, but specific to this worker.
@@ -466,7 +466,7 @@ added: v0.7.9
 
 * `worker` {cluster.Worker}
 * `code` {Number} the exit code, if it exited normally.
-* `signal` {String} the name of the signal (eg. `'SIGHUP'`) that caused
+* `signal` {String} the name of the signal (e.g. `'SIGHUP'`) that caused
   the process to be killed.
 
 When any of the workers die the cluster module will emit the `'exit'` event.