Update altgraph to 0.16.1

[pyup-bot]

This PR updates altgraph from 0.12 to 0.16.1.

Changelog

0.16.1

------

Explicitly mark Python 3.7 as supported in wheel metadata.

0.16

----

* Add LICENSE file

0.15

----

* ``ObjectGraph.get_edges``, ``ObjectGraph.getEdgeData`` and ``ObjectGraph.updateEdgeData``
accept *None* as the node to get and treat this as an alias for *self* (as other
methods already did).

0.14

----

- Issue 7: Remove use of ``iteritems`` in altgraph.GraphAlgo code

0.13

----

- Issue 4: Graph._bfs_subgraph and back_bfs_subgraph return subgraphs with reversed edges

Fix by "pombredanne" on bitbucket.

Links

• PyPI: https://pypi.org/project/altgraph
• Changelog: https://pyup.io/changelogs/altgraph/
• Docs: https://altgraph.readthedocs.io

[pyup-bot]

Closing this in favor of #92