pip break in Docker Ubuntu 14.04  build

 fix the  [Added additional required packages in requirements.txt](https://github.com/OpenBazaar/OpenBazaar/commit/224f12a371d4eaa36ee7955930c60704e31d61d9) and  [Bug #1363642 “pip breaks after upgrading python package requests : Bugs : “python-pip” package : Ubuntu](https://bugs.launchpad.net/ubuntu/+source/python-pip/+bug/1363642)