fix(extension): allow v4.1 to show in extension list

[gclough]

Fixes #69

Allows correct version to show in extension list after ALTER EXTENSION system_stats UPDATE;

pgtest_dev=# \dx system_stats
                          List of installed extensions
     Name     | Version | Schema |                  Description
--------------+---------+--------+-----------------------------------------------
 system_stats | 4.0     | public | EnterpriseDB system statistics for PostgreSQL
(1 row)

pgtest_dev=# ALTER EXTENSION system_stats UPDATE;
ALTER EXTENSION
pgtest_dev=# \dx system_stats
                          List of installed extensions
     Name     | Version | Schema |                  Description
--------------+---------+--------+-----------------------------------------------
 system_stats | 4.1     | public | EnterpriseDB system statistics for PostgreSQL
(1 row)

Also works on new creation:

pgtest_dev=# DROP EXTENSION system_stats;
DROP EXTENSION
pgtest_dev=# \dx system_stats
     List of installed extensions
 Name | Version | Schema | Description
------+---------+--------+-------------
(0 rows)

pgtest_dev=# CREATE EXTENSION system_stats;
CREATE EXTENSION
pgtest_dev=# \dx system_stats
                          List of installed extensions
     Name     | Version | Schema |                  Description
--------------+---------+--------+-----------------------------------------------
 system_stats | 4.1     | public | EnterpriseDB system statistics for PostgreSQL
(1 row)