Remove support for Python 3.4

[jcbrockschmidt]

Python 3.4 support has been removed in the latest versions of tox, as seen here.

Attempting to run tox 3.20.1 on better_profanity outputs the following log for the py34 tests:

ERROR: invocation failed (exit code 1), logfile: <OMITTED>/better_profanity/.tox/py34/log/py34-11.log
=============================== log start ================================
Traceback (most recent call last):
  File "/usr/lib/python3.4/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/__main__.py", line 16, in <module>
    from pip._internal.cli.main import main as _main  # isort:skip # noqa
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_internal/cli/main.py", line 10, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_internal/cli/autocompletion.py", line 9, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_internal/cli/main_parser.py", line 7, in <module>
    from pip._internal.cli import cmdoptions
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_internal/cli/cmdoptions.py", line 24, in <module>
    from pip._internal.exceptions import CommandError
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_internal/exceptions.py", line 10, in <module>
    from pip._vendor.six import iteritems
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_vendor/__init__.py", line 79, in <module>
    vendored("pkg_resources")
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pip/_vendor/__init__.py", line 36, in vendored
    __import__(modulename, globals(), locals(), level=0)
  File "/mnt/linux_storage/joshypoo/Projects/better_profanity/.tox/py34/lib/python3.4/site-packages/pkg_resources/__init__.py", line 92, in <module>
    raise RuntimeError("Python 3.5 or later is required")
RuntimeError: Python 3.5 or later is required

================================ log end =================================

The alternative seems to be using an older version of tox indefinitely.

[snguyenthanh]

Looks good. I think it's time to drop support for Python 3.4