SimpleCov merged reports are not processed correctly

[glebm]

At Thredded, we use SimpleCov and run rspec 3 times with different SimpleCov.command_name.

SimpleCov reports the coverage correctly:

Coverage report generated for test:js, test:migrations, test:nojs to /home/travis/build/thredded/thredded/coverage. 3584 / 3805 LOC (94.19%) covered.

However, CodeClimate doesn't seem to merge this correctly, as coverage shows up as 76%.

Example job: https://travis-ci.org/thredded/thredded/jobs/485054771
Configuration: https://github.com/thredded/thredded/blob/1fc37b67c4dfcd3d54b7f94268f79fc41e96035d/.travis.yml#L52-L65