Bump cryptography from 2.7 to 3.2

Bumps [cryptography](https://github.com/pyca/cryptography) from 2.7 to 3.2.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](pyca/cryptography@2.7...3.2)

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

requirements.txt

@@ -2,7 +2,7 @@
 altgraph==0.16.1
 asn1crypto==0.24.0
 cffi
-cryptography==2.7
+cryptography==3.2
 docopt==0.6.2
 fpdf==1.7.2
 future==0.17.1