Bump cryptography from 2.6.1 to 3.3.2 in /sandbox (#63)

Bumps [cryptography](https://github.com/pyca/cryptography) from 2.6.1 to 3.3.2.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst)
- [Commits](pyca/cryptography@2.6.1...3.3.2)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

sandbox/requirements.txt

@@ -1,6 +1,6 @@
 asn1crypto==0.24.0
 cffi==1.12.2
-cryptography==2.6.1
+cryptography==3.3.2
 dj-database-url==0.4.1
 Django==2.1.5
 django-argonauts==1.2.0