Bump cryptography from 3.3.1 to 3.4.3

Bumps [cryptography](https://github.com/pyca/cryptography) from 3.3.1 to 3.4.3.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](pyca/cryptography@3.3.1...3.4.3)

Signed-off-by: dependabot[bot] <support@github.com>

requirements-pinned.txt

@@ -1,7 +1,7 @@
 certifi==2020.12.5        # via requests
 cffi==1.14.4              # via cryptography, pynacl
 chardet==4.0.0            # via requests
-cryptography==3.3.1       # via securesystemslib
+cryptography==3.4.3       # via securesystemslib
 enum34==1.1.10            ; python_version < '3' # via cryptography
 idna==2.10                # via requests
 ipaddress==1.0.23         ; python_version < '3' # via cryptography