Update .travis.yml

[duddu]

Support multiple node.js jobs and minor optimizations

• putting node.js language outside the matrix let you run multiple versions-based jobs
• and join the install (yarn) phase in one line for all the jobs
• I set the same cache directories for all the jobs, since it's more concise, and having the empty .gradle/* folders cached for the not-android jobs does not affect the build process -- but it's purely a choice, you can also specify the cache explicitly for every job
• it's not clear if the "NODE_ENV" variable is ever used; if so, it should be overwritten in the android/ios job, otherwise it could be dropped from the node job

[duddu]

Unfortunately, travis doesn't pre-install yarn if an install phase is specified (see build #243), so I don't find another quick way to accomplish the second point for the moment. I made a second commit reverting to explicit install phase for android/ios

[krivachy]

Thank you @duddu! The changes look good and make sense. Off the top of my head I'm not quite sure either if NODE_ENV=test is used, but let's just leave it there just in case ;) Out of curiosity, why do you need node_js: false for the android/ios parts?

[duddu]

Yeah sorry I forgot to mention! The node_js=false are not really required, they just overwrite the property on main job, telling travis not to start the machine searching for node versions. They can be removed, the only real consequence is having a messed up job name for matrix jobs, like "Node.js 6.9,7.1 JDK: oraclejdk7" (multi-language matrix isn't really a standard yet...), though the job itself isn't affected. But If you prefer to remove them for code clarity I understand!

[krivachy]

No let's keep it, having clear job names is good.