Drop support for EOL Python 3.3

[hugovk]

Includes PR #1754.

Pytest, or rather py, has dropped support for Python 3.3 because it's EOL and little used (pytest-dev/py#165).

That is causing pylint builds to fail on Travis CI and AppVeyor.

Here's the pip installs for pylint from PyPI for the last month (via pypinfo --percent --pip pylint pyversion) showing a very low fraction for 3.3:

python_version	percent	download_count
2.7	60.7%	410,843
3.6	19.3%	130,802
3.5	11.6%	78,500
3.4	7.0%	47,680
2.6	0.8%	5,449
3.3	0.3%	1,703
3.7	0.2%	1,603
3.2	0.0%	31
None	0.0%	6

[hugovk]

Or should this be 2.0 if following semver?

[dmtucker]

Technically, yes, but python_requires kind of mitigates.

[PCManticore]

Thanks! We can have in 1.8, we don't do releases that often and we tend to cluster lots of big changes in minor releases. Unless it's something that completely changes how pylint works, we don't tend to jump to another major release.