Fix broken CI test, apply new lint rules

[Kroisse]

• Added maximum required versions to all test dependencies.
• Removed redundant flake8 execution. It will be run by pytest-flake8 plugin.
• Exit quitely on KeyboardInterrupt.

Blocks #11 and #14.

[dahlia]

If I remember correctly, it was intended to catch KeyboardInterrupt as well. It's better catch BaseException here IMO.

[Kroisse]

Catching BaseException is still harmful because BaseException includes non-error exceptions like StopIteration or GeneratorExit. I think it is better to catch Exception and KeyboardInterrupt explicitly.

[dahlia]

I think it's not the case here, because the only thing this except: clause does is just logging and reraising. What's your opinion?

[Kroisse]

In my opinion, it's much better to handle KeyboardInterrupt separately instead treating it as an error, since the situation when KeyboardInterrupt has been raised represents the obvious intention to abort this execution, not an unexpected failure.

[dahlia]

Although I approved, I don't have permission to merge this.

[Kroisse]

https://travis-ci.org/spoqa/geofront-cli/jobs/533189683

$ tox
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.3.6/bin/tox", line 7, in <module>
    from tox import cmdline
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/tox/__init__.py", line 32, in <module>
    from .session import cmdline  # isort:skip
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/tox/session/__init__.py", line 20, in <module>
    from tox.config import parseconfig
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/tox/config/__init__.py", line 18, in <module>
    import pkg_resources
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/pkg_resources/__init__.py", line 92, in <module>
    raise RuntimeError("Python 3.4 or later is required")
RuntimeError: Python 3.4 or later is required

……Time to consider dropping support for 3.3?

[dahlia]

Python 3.3 support now seems unrealistic. How about dropping this and bumping the minor version?

[Kroisse]

It makes sense.