Travis CI build stuck with failure on coverage

I do not understand why this build is running with coverage.

I already removed all coverage items from .travis.yml, cleared caches, and disabled cache in .travis.yml.

I must be missing something here, I just want to turn it off to fix my builds.

This is a part of npm test functionality and/or the proof test framework that you are using.
I would use their debug facilities to understand why the command is failing despite the test seemingly succeeding.