Regression tests mismatch when running in Travis

[dami-gg]

When running visual regression tests in Travis CI, we get some errors on some components, for example:

https://travis-ci.org/zalando/dress-code/jobs/337491564

After some investigation, it could be related to differences in font rendering in different OS, since the current baseline is created in our Mac machines and Travis is running Ubuntu:

https://github.com/Huddle/PhantomCSS/issues/22

It is actually really hard to figure out right now what's the diff found since Travis discards the instance right after it finished. It would be really useful to try to publish the failures somewhere so we could check in case an error happens. This article proposes a possible solution:

https://twolfson.com/2014-02-25-visual-regression-testing-in-travis-ci