Update pylint to 1.9.1

[pyup-bot]

This PR updates pylint from 1.8.4 to 1.9.1.

Changelog

1.9

=========================

Release date: 2018-05-15

 * Added two new Python 3 porting checks, `exception-escape` and `comprehension-escape`

   These two are emitted whenever pylint detects that a variable defined in the
   said blocks is used outside of the given block. On Python 3 these values are deleted.

 * Added a new `deprecated-sys-function`, emitted when accessing removed sys members.

 * Added `xreadlines-attribute`, emitted when the `xreadlines()` attribute is accessed.

 * The Python 3 porting mode can now run with Python 3 as well.

 * docparams extension allows abstract methods to document what overriding
   implementations should return, and to raise NotImplementedError without
   documenting it.

   Closes 2044

 * Special methods do not count towards `too-few-methods`,
   and are considered part of the public API.

 * Enum classes do not trigger `too-few-methods`

   Close 605

 * Added a new Python 2/3 check for accessing `operator.div`, which is removed in Python 3

   Close 1936

 * Added a new Python 2/3 check for accessing removed urllib functions

   Close 1997

Links

• PyPI: https://pypi.org/project/pylint
• Changelog: https://pyup.io/changelogs/pylint/
• Repo: https://github.com/PyCQA/pylint

[pyup-bot]

Closing this in favor of #16