replaced with more meaningful example

dataset/persistence/table.py

@@ -173,7 +173,7 @@ class Table(object):
         ``type`` must be a `SQLAlchemy column type <http://docs.sqlalchemy.org/en/rel_0_8/core/types.html>`_.
         ::
 
-            table.create_column('person', sqlalchemy.String)
+            table.create_column('created_at', sqlalchemy.DateTime)
         """
         with self.database.lock:
             if name not in self.table.columns.keys():