Intermittent build errors with "curl: (60) SSL certificate problem: Invalid certificate chain"

build-env
#1

Getting subj from time to time. Sample failure: https://travis-ci.org/skvark/opencv-python/jobs/455657108 .

I used to blame my caching logic, but this time, the error happened before any caches were even loaded!

It looks like some build slaves have a problem with their OSX installation.