Requests 2.6 introduced this warning for users of python prior to 2.7.9 with only stock SSL modules available.
Assuming you can't upgrade to a newer version of python, this will install more up-to-date python SSL libraries:
pip install --upgrade ndg-httpsclient
HOWEVER, this may fail on some systems without the build-dependencies for pyOpenSSL. On debian systems, running this before the pip command above should be enough for pyOpenSSL to build:
apt-get install python-dev libffi-dev libssl-dev