更新樣板
更新樣板

* Update navbar and toggle to Bootstrap 4 HTML.
  https://github.com/pydanny/cookiecutter-django/commit/8330706775bb6c996db6252e5874bd39421d1e96
* Update stylesheet to Bootstrap 4. Remove optional theme stylesheet.
  https://github.com/pydanny/cookiecutter-django/commit/968c04369e21cd2e6024bfea6a8ef777ed7b9a0f
* Remove navbar's corners, and invert colors.
  https://github.com/pydanny/cookiecutter-django/commit/69617648d5e6b61604b9b093eb887c0322ba393e
* Be consistent with using non-fluid container in base template.
  https://github.com/pydanny/cookiecutter-django/commit/15dd4007695a919b99e24a9c4d3f30330ab7e324
* Upgrade jQuery to 2.1.4 and Bootstrap JS to Bootstrap 4.
  https://github.com/pydanny/cookiecutter-django/commit/243e823a2efbddbcf26ac000dedbd9d9a004edcb
* Put <nav> into a div with a nicer-displaying bottom margin.
  https://github.com/pydanny/cookiecutter-django/commit/139deaf6b80b74ca4220bcc25f399fc4ec78a622
* update AngularJS version to 1.4.4
  https://github.com/pydanny/cookiecutter-django/commit/ebc728613e4e338084a3447d6aed388b27e2443c

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