An in-range update of acorn is breaking the build 🚨

## The dependency [acorn](https://github.com/acornjs/acorn) was updated from `6.0.2` to `6.0.3`.

🚨 [View failing branch](https://github.com/ForbesLindesay/acorn-globals/compare/master...ForbesLindesay:greenkeeper%2Facorn-6.0.3).

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




acorn is a direct dependency of this project, and **it is very likely causing it to break**. If other packages depend on yours, this update is probably also breaking those in turn.



<details>
<summary>Status Details</summary>

- ❌ **continuous-integration/travis-ci/push:** The Travis CI build failed ([Details](https://travis-ci.org/ForbesLindesay/acorn-globals/builds/450485250?utm_source=github_status&utm_medium=notification)).
</details>


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<details>
<summary>FAQ and help</summary>

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