An in-range update of @types/chai is breaking the build 🚨

Nobody has claimed this yet.

## The devDependency [@types/chai](https://github.com/DefinitelyTyped/DefinitelyTyped) was updated from `4.1.7` to `4.2.0`.

🚨 [View failing branch](https://github.com/linkedin/opticss/compare/master...linkedin:greenkeeper%2Fdefault%2F%40types%2Fchai-4.2.0).

This version is **covered** by your **current version range** and after updating it in your project **the build failed**.

@types/chai is a devDependency of this project. It **might not break your production code or affect downstream projects**, but probably breaks your build or test tools, which may **prevent deploying or publishing**.

Status Details

- ❌ **continuous-integration/travis-ci/push:** The Travis CI build failed ([Details](https://travis-ci.org/linkedin/opticss/builds/569686611?utm_source=github_status&utm_medium=notification)).

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FAQ and help

There is a collection of [frequently asked questions](https://greenkeeper.io/faq.html). If those don’t help, you can always [ask the humans behind Greenkeeper](https://github.com/greenkeeperio/greenkeeper/issues/new).

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Your [Greenkeeper](https://greenkeeper.io) Bot :palm_tree:

Start with the failing Greenkeeper branch and the Travis CI build details to identify the failure caused by updating @types/chai from 4.1.7 to 4.2.0. Trace the affected build or test command and confirm completion when the project builds successfully with a compatible dependency update or resolution.

Written by the indexing model from the issue text.