Bump astroid from 2.1.0 to 2.2.1 in /requirements

[dependabot-preview]

Bumps astroid from 2.1.0 to 2.2.1.

Changelog

Sourced from astroid's changelog.

What's New in astroid 2.2.1?

Release Date: 2019-03-02

• Make sure to infer the arguments to the slice() builtin

Close pylint-dev/pylint#2770

• Correctly instantiate exception instances when inferring their attributes with objectmodel

Close pylint-dev/pylint#2776

What's New in astroid 2.2.0?

Release Date: 2019-02-27

• Fix a bug concerning inference of calls to numpy function that should not return Tuple or List instances.

Close pylint-dev/pylint#2436

• typed_ast gets installed for Python 3.7, meaning type comments can now work on 3.7.

• Fix a bug concerning inference of unary operators on numpy types.

  Close False positive E1130 invalid-unary-operand-type for Numpy array pylint-dev/pylint#2436 (first part)

• Fix a crash with typing.NamedTuple and empty fields. Close "invalid syntax" on typing.NamedTuple pylint-dev/pylint#2745

• Add a proper strerror inference to the OSError exceptions.

  Close E1101: Class 'strerror' has no 'lower' member (no-member) pylint-dev/pylint#2553

• Support non-const nodes as values of Enum attributes.

  Close #612

• Fix a crash in the enum brain tip caused by non-assign members in class definitions.

  Close AENUM creating class bodies dynamically causes pylint warning pylint-dev/pylint#2719

• brain_numpy returns an undefined type for numpy methods to avoid assignment-from-no-return

  Close numpy.logical_or gives false error assignment-from-no-return pylint-dev/pylint#2694

• Fix a bug where a call to a function that has been previously called via
  functools.partial was wrongly inferred

  Close Using functools partial on a function gives a too-many-function-args when using the function pylint-dev/pylint#2588

... (truncated)

Commits

• 2caa1b3 Prepare 2.2.1
• 8a3d8b9 Correctly instantiate exception instances when inferring their attributes wit...
• 13790cc Open up 2.2.1 and add changelog entry for the slice() fix
• 2021865 Make sure to infer the arguments to the slice() builtin
• 9eddca3 When picking the parse function, make sure to parse with the right minor version
• 87db3f5 Disable test that does not make sense on versions older than Python 3.6
• 9b6445d Prepare 2.2.0
• e5fe824 Remove merge marker
• cee7875 Don't clear the manager caching any longer
• 08cbcba Use the right pytest methods for setup and teardown
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #155.