Update cryptography requirement from ~=3.1.0 to ~=3.4.7

Created by: dependabot[bot]

Updates the requirements on cryptography to permit the latest version.

Changelog

Sourced from cryptography's changelog.

3.4.7 - 2021-03-25

* Updated Windows, macOS, and ``manylinux`` wheels to be compiled with
  OpenSSL 1.1.1k.
.. _v3-4-6:
3.4.6 - 2021-02-16

• Updated Windows, macOS, and manylinux wheels to be compiled with OpenSSL 1.1.1j.

.. _v3-4-5:

3.4.5 - 2021-02-13

* Various improvements to type hints.
* Lower the minimum supported Rust version (MSRV) to >=1.41.0. This change
  improves compatibility with system-provided Rust on several Linux
  distributions.
* ``cryptography`` will be switching to a new versioning scheme with its next
  feature release. More information is available in our
  :doc:`/api-stability` documentation.
.. _v3-4-4:
3.4.4 - 2021-02-09

• Added a py.typed file so that mypy will know to use our type annotations.
• Fixed an import cycle that could be triggered by certain import sequences.

.. _v3-4-3:

3.4.3 - 2021-02-08

* Specify our supported Rust version (>=1.45.0) in our ``setup.py`` so users
  on older versions will get a clear error message.
.. _v3-4-2:
3.4.2 - 2021-02-08

• Improvements to make the rust transition a bit easier. This includes some

... (truncated)

Commits

• a19014a Prep for 3.4.7 release (#5933)
• 75b002a Release 346 (#5840)
• 4d77fb9 3.4.5 backports and changelog/version bump (#5827)
• 4a3018e 3.4.4 - backports, changelog, and version bumps (#5803)
• 86c9e4a version bump, changelog already done (#5791)
• 0f40cb3 [3.4] Specify an MSRV in setup.py (#5789) (#5790)
• 74a3df4 3.4.2 changelog and version bump (#5784)
• 4a66e2b [3.4] More aggressively point people at Rust version docs (#5782) (#5783)
• 843ada6 Remove setuptools_rust from install requirement (#5779) (#5781)
• e5b5c3d Interface: Make annotation check optional (#5775) (#5780)
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot close will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)