Log Message:
Update py-flask-assets to 0.12.

0.12 (2016-08-18)
    - Added registration of Flask CLI commands using `flask.commands`
      entrypoint group. (Jiri Kuncar)
    - Added an optional support for FlaskAzureStorage when
      `FLASK_ASSETS_USE_AZURE` is set.  (Alejo Arias)
    - Updated Flask extension imports for compatibility with Flask 0.11.
      (Andy Driver) (fixes #102)
    - Fixed generation of absolute urls using //. (fixes #73)
    - Fixed Flask-Script assets build command. (Frank Tackitt)