travis do only 2 builds

[jangorecki]

Closes #3357
it takes now 20min. Osx build is slow, takes 15min, probably because of installing llvm each time. @MarcusKlik any idea if we can cache that somehow?

[jangorecki]

_R_CHECK_CRAN_INCOMING_REMOTE_=false defined below should resolve problem of slow --as-cran

[jangorecki]

ideally this install llvm we would like to speed up

[MarcusKlik]

Hi @jangorecki ,

yes, I see that the llvm installation takes almost 5 minutes, that's quite long!
The same is true for the brew update command at the start of the build, that one also takes a bite out of the total running time.

We could cache the homebrew directory to cache the homebrew package downloads:

cache:
  directories:
    - $HOME/Library/Caches/Homebrew

before_cache:
  - brew cleanup

But as Travis stores the cache at a storage provider (see this doc), I don't think that downloading from the cache will be much faster than a direct download.

Also, following the Travis documentation on caching it seems that we should be able to cache the llvm installation directory itself, but somehow homebrew fails to install llvm correctly on the cached (initially empty) directory.

Some more testing to be done I think...

[jangorecki]

Thanks @MarcusKlik for detailed answer on that. I think we can also remove test coverage report from OSX build. It takes 330s and linux test coverage should be enough.