Fix CI in MacOS

[Alexander Vershilov]

Currently MacOS CI fails with:

Collecting ipython
  Downloading ipython-6.2.1.tar.gz (5.1MB)
    100% |████████████████████████████████| 5.1MB 131kB/s 
    Complete output from command python setup.py egg_info:
    
    IPython 6.0+ does not support Python 2.6, 2.7, 3.0, 3.1, or 3.2.
    When using Python 2.7, please install IPython 5.x LTS Long Term Support version.
    Beginning with IPython 6.0, Python 3.3 and above is required.
    
    See IPython `README.rst` file for more information:
    
        https://github.com/ipython/ipython/blob/master/README.rst
    
    Python sys.version_info(major=2, minor=7, micro=12, releaselevel='final', serial=0) detected.
    Your pip version is out of date, please install pip >= 9.0.1. pip 8.1.2 detected.

We need to either switch to a newer python or use older IPython.

[Alexander Vershilov]

Addressed by the #311.