Travis for Mac OS

[theaquamarine]

Builds on the Linux config in #524, from #302.

Mac OS builds report the same errors as Linux (which makes sense, since from a PowerShell perspective they're about identical), so adding it as a target may not be desirable, given the very long queue lengths Travis normally has- a couple of hours at the moment. Travis won't report back to GitHub until both builds are done, but results for Linux and Mac OS can be seen separately on the actual build page.

[dahlbyk]

Is it possible to only trigger Mac builds on develop, as a sanity check, but not on PRs?

[theaquamarine]

Ok, that appears to be working. It's going to build on Mac OS for this pull against develop, but not on my Travis branch.

[dahlbyk]

This latest Travis build seems to be stalled: https://travis-ci.org/dahlbyk/posh-git/builds/328463756. Linux failed fast, but it appears to be waiting for the Mac build to start?

[dahlbyk]

Check out https://stackoverflow.com/a/47734517/54249

[theaquamarine]

Yeah, that's the delay in the job queue for a Mac OS VM. It'll list the build as started, not returning success or failure until the Mac OS build is at least attempted. Eventually the Mac OS job will run and Travis will report success/failure, but it can take a while- this one waited over three hours to get to the head of the queue, the last commit in this PR took nearly two, and I've had several wait longer than that. The status page suggests their Mac OS builds are pretty much always backlogged.

We could try narrowing the condition more, but I can't think of anything that'd make Travis return faster other than dropping Mac OS entirely- which is probably reasonable since Linux is going to be pretty close and builds in a matter of seconds. Making Travis only run Mac OS if Linux passes would help us now, but won't be much use once the existing failures get sorted.

[theaquamarine]

1 hour 50 minutes for that to finish.