Issue/pin cryptography dependency

Created by: arnaudsjs

Description

Pin cryptography dependency to the correct version

Linked to inmanta/infra-tickets#93

Self Check:

• Attached issue to pull request
• Changelog entry
• Version number is bumped to dev version
• Code is clear and sufficiently documented
• Sufficient test cases (reproduces the bug/tests the requested feature)
• Correct, in line with design
• End user documentation is included or an issue is created for end-user documentation

Reviewer Checklist:

• Sufficient test cases (reproduces the bug/tests the requested feature)
• Code is clear and sufficiently documented
• Correct, in line with design