Fixed : Improved downloading of requirements.txt

[kunalsz]

in reference to the issue #45

This PR updates the honeyscanner/honeypots/base_honeypot.py

Changes made:

• The versions and requirements.txt were hard coded, not covering latest versions released which is not scalable enough
• A new function get_requirements is added to the BaseHoneypot class which retrieves the latest version and requirements.txt file of a honeypot
• cowrie.py and conpot.py were updated as they have requirements.txt on their GitHub repo.

The error has been fixed and the code has been made more scalable