Rename W4_manytomany.py to roster.py

Author: xchen012

W4_manytomany.py roster.pyW4_manytomany.py renamed to roster.py

@@ -67,4 +67,4 @@
         (user_id, course_id, role) VALUES ( ?, ?, ? )''', 
         ( user_id, course_id, role ) )
 
-    conn.commit()
+    conn.commit()