fix: check if module.paths really exists

[ematipico]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions.

Description of the Change

module.paths was not defined when Mocha was run in an serverless environment. Probably due to the absence of node_modules folder. I had bundled the test using a bundler.

I added a check to make sure it doesn't throw an error.

Alternate Designs

Not sure if there are any other alternatives but open to suggestions.

Why should this be in core?

I don't think userland should mock module.paths.

Benefits

It would not throw an error during the execution of tests in a serverless environment.

Possible Drawbacks

I don't see any.

Applicable issues

Fixes #2505
This should be a bug fix

[coveralls]

Coverage increased (+0.002%) to 92.903% when pulling e548131 on ematipico:bugfix/module-paths into 4dc3cd1 on mochajs:master.

[outsideris]

Serverless means AWS Lambda or Google Cloud Functions?

[ematipico]

In my particular case, AWS Lambda

[boneskull]

Thanks, LGTM