Bump cryptography from 2.5 to 3.2

Bumps [cryptography](https://github.com/pyca/cryptography) from 2.5 to 3.2.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pyca/cryptography/compare/2.5...3.2)

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

setup.py

@@ -21,7 +21,7 @@ setup(
         'aiohttp',
         'aiojobs',
         'ecdsa>=0.13.3',
-        'cryptography==2.5',
+        'cryptography==3.2',
         'PyNaCl>=1.3.0',
         'requests',
         'cython',