[scikit-image] Daily wheel builds

Hi, I just set up daily wheel builds for scikit-image master. They run via travis-ci cron jobs, and have the dual role of testing that wheel building works, as well as testing on 32-bit Linux, and several macOS versions. The wheel builds run from the "daily" branch of the scikit-image-wheels repo: https://github.com/scikit-image/scikit-image-wheels/tree/daily See here for logs of the daily builds: https://travis-ci.org/scikit-image/scikit-image-wheels/branches The build exposed a few test failures on 32-bit - see: https://github.com/scikit-image/scikit-image/issues/2670 Cheers, Matthew