Additional bears test fails frequently

Some builds are failing in the additional bears test. i.e. using `NoCommentsBear` here:

https://github.com/coala/docker-coala-base/blob/master/hooks/test#L37

Start with hooks/test at the linked line and inspect how the additional bears test invokes NoCommentsBear. Run the test repeatedly in the project’s build environment to identify the intermittent failure; done means the additional bears test passes reliably across builds.

Written by the indexing model from the issue text.