Bump cryptography from 1.9 to 3.2

Bumps [cryptography](https://github.com/pyca/cryptography) from 1.9 to 3.2.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](pyca/cryptography@1.9...3.2)

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

requirements.txt

@@ -15,7 +15,7 @@ click==6.7
 colorama==0.3.9
 coverage==4.5.1
 coveralls==1.3.0
-cryptography==1.9
+cryptography==3.2
 docopt==0.6.2
 flake8==3.5.0
 Flask==0.12.2