Update AUTHORS.txt

Adding Sertan Senturk's contact details

Author: sertansenturk

AUTHORS.txt

@@ -49,5 +49,5 @@ This toolbox contains patches submitted by the following contributors:
 - Insik Kim <insik92 at gmail.com>
   (Pull#12) Bug fix: Resolving bug that cell type is converted to json with transposed data
 
-- Sertan Senturk 
-  (Pull#10,#11)  Feature: Added matlab object saving to savejson and saveubjson
+- Sertan Senturk <contact at sertansenturk.com>
+  (Pull#10,#11) Feature: Added matlab object saving to savejson and saveubjson