python 3.4 deprecated

[n2ygk]

Python 3.4 is dropped by upstream DRF per encode/django-rest-framework#6620

We should drop it from DJA as well.

DEPRECATION: Python 3.4 support has been deprecated. pip 19.1 will be the last one supporting it. Please upgrade your Python as Python 3.4 won't be maintained after March 2019 (cf PEP 429).
Collecting https://github.com/encode/django-rest-framework/archive/master.zip
  Downloading https://github.com/encode/django-rest-framework/archive/master.zip
    ERROR: Complete output from command python setup.py egg_info:
    ERROR: 
    ==========================
    Unsupported Python version
    ==========================
    
    This version of Django REST Framework requires Python 3.5, but you're trying
    to install it on Python 3.4.
    
    This may be because you are using a version of pip that doesn't
    understand the python_requires classifier. Make sure you
    have pip >= 9.0 and setuptools >= 24.2, then try again:
    
        $ python -m pip install --upgrade pip setuptools
        $ python -m pip install djangorestframework
    
    This will install the latest version of Django REST Framework which works on
    your version of Python. If you can't upgrade your pip (or Python), request
    an older version of Django REST Framework:
    
        $ python -m pip install "django<3.10"
    ----------------------------------------