Fix a typo on User agent library.
diff --git a/system/libraries/User_agent.php b/system/libraries/User_agent.php
index 0b77a7d..2cdaf50 100644
--- a/system/libraries/User_agent.php
+++ b/system/libraries/User_agent.php
@@ -18,7 +18,7 @@
 /**
  * User Agent Class
  *
- * Identifies the platform, browser, robot, or mobile devise of the browsing agent
+ * Identifies the platform, browser, robot, or mobile device of the browsing agent
  *
  * @package		CodeIgniter
  * @subpackage	Libraries
@@ -546,4 +546,4 @@
 
 
 /* End of file User_agent.php */
-/* Location: ./system/libraries/User_agent.php */
\ No newline at end of file
+/* Location: ./system/libraries/User_agent.php */