Update psycopg2 to 2.7.6 (#1311)
Update psycopg2 to 2.7.6 (#1311)

This PR updates [psycopg2](https://pypi.org/project/psycopg2) from **2.7.5** to **2.7.6**.



<details>
  <summary>Changelog</summary>
  
  
   ### 2.7.6
   ```
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^

- Close named cursors if exist, even if `~cursor.execute()` wasn&#39;t called
  (:ticket:`746`).
- Fixed building on modern FreeBSD versions with Python 3.7 (:ticket:`755`).
- Fixed hang trying to :sql:`COPY` via `~cursor.execute()` (:ticket:`781`).
- Fixed adaptation of arrays of empty arrays (:ticket:`788`).
- Fixed segfault accessing the `connection.readonly` and
  `connection.deferrable` repeatedly (:ticket:`790`).
- `~psycopg2.extras.execute_values()` accepts `~psycopg2.sql.Composable`
  objects (794).
- `~psycopg2.errorcodes` map updated to PostgreSQL 11.
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/psycopg2
  - Changelog: https://pyup.io/changelogs/psycopg2/
  - Homepage: http://initd.org/psycopg/
</details>


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