[#482] Fix SSR issues when accessing document object

[stefcameron]

Fixes #482

PR Checklist

Please leave this checklist in your PR.

• Issue being fixed is referenced.
• Source changes maintain:
  • Stated browser compatibility.
  • Stated React compatibility.
• Unit test coverage added/updated.
• E2E test coverage added/updated.
• Prop-types added/updated.
• Typings added/updated.
• README updated (API changes, instructions, etc.).
• Changes to dependencies explained.
• Changeset added (run yarn changeset locally to add one, and follow the prompts).
  • EXCEPTION: A Changeset is not required if the change does not affect any of the source files that produce the package bundle. For example, tooling changes, test updates, or a new dev-only dependency to run tests more efficiently should not have a Changeset since it will not affect package consumers.

[changeset-bot]

🦋 Changeset detected

Latest commit: 46468bc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
focus-trap-react	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR