You are using pip version 8.1.1, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

pip install --upgrade pip

Collecting pip
  Using cached pip-9.0.1-py2.py3-none-any.whl
Installing collected packages: pip
Successfully installed pip-8.1.1
You are using pip version 8.1.1, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

sudo apt-get update

sudo apt-get upgrade

wget https://bootstrap.pypa.io/get-pip.py

sudo python get-pip.py

pip --version

pip 9.0.1 from /home/ubuntu/.local/lib/python2.7/site-packages (python 2.7)