Update Pylint

Our current version of pylint is slightly out of date and we're missing out on some bug fixes from the newer versions.

```
❯ pylint --version
pylint 1.6.5,
astroid 1.4.0
```

One example is https://github.com/box/ClusterRunner/pull/394#discussion-diff-129183853R73
in our code where there's a problem with type annotating tuples. More about that particular issue can be found at https://github.com/PyCQA/pylint/issues/1212

We should update pylint at some point and then remove the disable workarounds. The particular issue mentioned here looks like it was fixed in version 1.5 for astroid.