Merge pull request #234 from johnbellone/issue31

Fix #31: Changing to set as add will not save over existing value
diff --git a/system/libraries/Cache/drivers/Cache_memcached.php b/system/libraries/Cache/drivers/Cache_memcached.php
index ae9d6cd..04aa81a 100644
--- a/system/libraries/Cache/drivers/Cache_memcached.php
+++ b/system/libraries/Cache/drivers/Cache_memcached.php
@@ -64,7 +64,7 @@
 	 */
 	public function save($id, $data, $ttl = 60)
 	{
-		return $this->_memcached->add($id, array($data, time(), $ttl), $ttl);
+		return $this->_memcached->set($id, array($data, time(), $ttl), $ttl);
 	}
 
 	// ------------------------------------------------------------------------