Bump cryptography from 2.1.4 to 2.3

Bumps [cryptography](https://github.com/pyca/cryptography) from 2.1.4 to 2.3.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](pyca/cryptography@2.1.4...2.3)

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

Author: dependabot[bot]

requirements.txt

@@ -17,7 +17,7 @@ cffi==1.12.3
 chardet==3.0.4
 Click==7.0
 colorclass==2.2.0
-cryptography==2.1.4
+cryptography==2.3
 cymem==2.0.2
 decorator==4.4.0
 defusedxml==0.6.0