minor #1186 Update session_storage.rst: Add missing lifetime column (andytruong)

This PR was merged into the 2.0.x-dev branch.

Discussion
----------

Update session_storage.rst: Add missing lifetime column

Commits
-------

e85ec346 Update session_storage.rst

doc/cookbook/session_storage.rst

@@ -66,6 +66,7 @@ have to make another database connection, simply pass the getWrappedConnection m
         'db_table'        => 'session',
         'db_id_col'       => 'session_id',
         'db_data_col'     => 'session_value',
+        'db_lifetime_col' => 'session_lifetime',
         'db_time_col'     => 'session_time',
     );
 
@@ -84,6 +85,7 @@ PdoSessionStorage needs a database table with 3 columns:
 
 * ``session_id``: ID column (VARCHAR(255) or larger)
 * ``session_value``: Value column (TEXT or CLOB)
+* ``session_lifetime``: Lifetime column (INTEGER)
 * ``session_time``: Time column (INTEGER)
 
 You can find examples of SQL statements to create the session table in the