Coveralls: pass it PR number
Coveralls: pass it PR number

`TRAVIS_PULL_REQUEST` contains either a PR number, or "false" for non-PR
pushes, so it makes no sense to compare it to "true". This PR instead
makes a non-equals comparison to "false".

der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,newsboat/newsboat