Bump astroid from 1.6.4 to 2.2.0

Bumps [astroid](https://github.com/PyCQA/astroid) from 1.6.4 to 2.2.0.
- [Release notes](https://github.com/PyCQA/astroid/releases)
- [Changelog](https://github.com/PyCQA/astroid/blob/master/ChangeLog)
- [Commits](pylint-dev/astroid@astroid-1.6.4...astroid-2.2.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

requirements.txt

@@ -1,5 +1,5 @@
 alembic==0.9.9
-astroid==1.6.4
+astroid==2.2.0
 autopep8==1.3.5
 certifi==2018.4.16
 chardet==3.0.4