Bump cryptography from 2.7 to 3.2 in /app

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](https://github.com/pyca/cryptography/compare/2.7...3.2)

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

app/requirements.txt

@@ -8,7 +8,7 @@ chardet==3.0.4
 Click==7.0
 colorclass==2.2.0
 CouchDB==1.2
-cryptography==2.7
+cryptography==3.2
 docopt==0.6.2
 dominate==2.4.0
 Flask==1.1.1