fix(ci): the Travis CI failed

[matteobertoldo]

Describe the bug

Every time the CI is launched this error appears:
https://app.travis-ci.com/github/matteobertoldo/atomforce/jobs/568662928#L427.

To Reproduce

Steps to reproduce the behavior:

1. Commit to master branch

Expected behavior

No errors in CI.

Screenshots

None.

Desktop (please complete the following information):

• OS: Travis CI ATOM_CHANNEL=beta Linux Xenial

Additional context

None.