Break out at the moment of concatenate with other files

Environment:
- Preview version: 1.29.0
- Browser name and version: Google Chrome Versión 63.0.3239.132
- Operating system and version: Windows 10

Steps to reproduce the problem:
1. yarn run prod
2. Concatenate with other JS files

What is the expected behavior?
The box-content-preview library should work when is concatenated with another JS

What went wrong?
At the moment when the library its concatenated with other ones show this message

We're using your library in our project. In dev mode we're including all files listed and works just fine.
But when we build for production, our process takes all JS and minifies and concat all files in a single one (builtApp.js)
At this point, there is a check (https://github.com/box/box-content-preview/blob/master/src/lib/util.js#L603) for a `