[ci skip] Fix incorrect wording in config.php

Related: 9e82b0d00cbe83d6cdfa914628023cb98d70c933
diff --git a/application/config/config.php b/application/config/config.php
index d0cfdfa..1474055 100644
--- a/application/config/config.php
+++ b/application/config/config.php
@@ -336,7 +336,7 @@
 | Encryption Key
 |--------------------------------------------------------------------------
 |
-| If you use the Encryption class, you must set the an encryption key.
+| If you use the Encryption class, you must set an encryption key.
 | See the user guide for more info.
 |
 | http://codeigniter.com/user_guide/libraries/encryption.html