Adding in .ics MIME type for calendar invites.
diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index 48c3bf3..103c3cb 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1891,6 +1891,7 @@
 						'tiff'	=>	'image/tiff',
 						'tif'	=>	'image/tiff',
 						'css'	=>	'text/css',
+						'ics'	=>	'text/calendar',
 						'html'	=>	'text/html',
 						'htm'	=>	'text/html',
 						'shtml'	=>	'text/html',