Update flask requirement from ~=1.1.2 to ~=2.0.0

[dependabot]

Updates the requirements on flask to permit the latest version.

Release notes

Sourced from flask's releases.

2.0.0

New major versions of all the core Pallets libraries, including Flask 2.0, have been released! 🎉

• Read the announcement on our blog: https://palletsprojects.com/blog/flask-2-0-released/
• Read the full list of changes: https://flask.palletsprojects.com/changes/#version-2-0-0
• Retweet the announcement on Twitter: https://twitter.com/PalletsTeam/status/1392266507296514048
• Follow our blog, Twitter, or GitHub to see future announcements.

This represents a significant amount of work, and there are quite a few changes. Be sure to carefully read the changelog, and use tools such as pip-compile and Dependabot to pin your dependencies and control your updates.

Changelog

Sourced from flask's changelog.

Version 2.0.0

Released 2021-05-11

• Drop support for Python 2 and 3.5.
• Bump minimum versions of other Pallets projects: Werkzeug >= 2, Jinja2 >= 3, MarkupSafe >= 2, ItsDangerous >= 2, Click >= 8. Be sure to check the change logs for each project. For better compatibility with other applications (e.g. Celery) that still require Click 7, there is no hard dependency on Click 8 yet, but using Click 7 will trigger a DeprecationWarning and Flask 2.1 will depend on Click 8.
• JSON support no longer uses simplejson. To use another JSON module, override app.json_encoder and json_decoder. :issue:3555
• The encoding option to JSON functions is deprecated. :pr:3562
• Passing script_info to app factory functions is deprecated. This was not portable outside the flask command. Use click.get_current_context().obj if it's needed. :issue:3552
• The CLI shows better error messages when the app failed to load when looking up commands. :issue:2741
• Add :meth:sessions.SessionInterface.get_cookie_name to allow setting the session cookie name dynamically. :pr:3369
• Add :meth:Config.from_file to load config using arbitrary file loaders, such as toml.load or json.load. :meth:Config.from_json is deprecated in favor of this. :pr:3398
• The flask run command will only defer errors on reload. Errors present during the initial call will cause the server to exit with the traceback immediately. :issue:3431
• :func:send_file raises a :exc:ValueError when passed an :mod:io object in text mode. Previously, it would respond with 200 OK and an empty file. :issue:3358
• When using ad-hoc certificates, check for the cryptography library instead of PyOpenSSL. :pr:3492
• When specifying a factory function with FLASK_APP, keyword argument can be passed. :issue:3553
• When loading a .env or .flaskenv file, the current working directory is no longer changed to the location of the file. :pr:3560
• When returning a (response, headers) tuple from a view, the headers replace rather than extend existing headers on the response. For example, this allows setting the Content-Type for jsonify(). Use response.headers.extend() if extending is desired. :issue:3628
• The Scaffold class provides a common API for the Flask and Blueprint classes. Blueprint information is stored in attributes just like Flask, rather than opaque lambda functions. This is intended to improve consistency and maintainability. :issue:3215
• Include samesite and secure options when removing the session cookie. :pr:3726

... (truncated)

Commits

• 2f0c62f Merge pull request #4007 from pallets/release-2.0.0
• f8e63d3 release version 2.0.0
• 1403d35 update type annotations
• 3a5532b update pallets projects minimum versions
• f8f0caf update requirements
• 9c1e7f6 Merge pull request #4005 from pallets/pre-commit-ci-schedule
• 8b72f6a update pre-commit monthly
• 28262c3 Merge pull request #3999 from greyli/improve-cli-docs
• 531671c Improve the wording of using FLASK_APP
• 2c88e8a Merge pull request #4003 from pallets/autodoc-typehints
• Additional commits viewable in compare view

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[dependabot]

Superseded by #272.