Mac builds on Travis CI is too slower than Linux builds

[dahlia]

Whereas Linux builds tend to take shorter than 15 minutes, Mac builds take longer than 30 minutes. Mostly twice longer. It seems that Mac builds less hit cache.

[dahlia]

Since it isn't due to cache misses as I replied in #120, I won't make any effort to fix this. It might would better switch to an other hosted CI service.

Seems it's not due to cache misses, but Travis CI's own problem:

@travisci i think you really need to invest into more osx builders. It takes ages even to get a builder

— Armin Ronacher (@mitsuhiko) February 8, 2017

@mitsuhiko Actually, we are and we're working on getting them available for use! Should be soon enough to see some improvements here... 💛

— Travis CI (@TravisCI) February 8, 2017

Our @GitKraken OSX builds are continuously taking longer @travisci. +1 hour now while linux is < 15 min. They used to be the same.

— John Haley (@johnhaley81) March 9, 2017

[dahlia]

Nowadays it work quite well.