CA Certificates
By default Requests bundles a set of root CAs that it trusts, sourced from the Mozilla trust store.
However, these are only updated once for each Requests version. This means that if you pin a
Requests version your certificates can become extremely out of date.
From Requests version 2.4.0 onwards, Requests will attempt to use certificates from certifi if it is
present on the system. This allows for users to update their trusted certificates without having to
change the code that runs on their system.
For the sake of security we recommend upgrading certifi frequently!
Citing http://docs.python-requests.org/en/latest/user/advanced/