Switch to private IPs for Mac VMs for now

There's a firewall issue causing the workers to connect to VMs when they
are being run on the VM host. Once the workers are being moved off the
VM host we can switch back to public IPs.
update travis-build
if we have trouble figuring out what template to use, don't explode
Merge branch 'master' of https://github.com/travis-ci/travis-worker
Updated Rakefile to match README.md
Merge pull request #75 from Aaron1011/update_rakefile

Updated Rakefile to match README.md
And then 'cancel job' was born
Merge branch 'master' of https://github.com/travis-ci/travis-worker
Merge branch 'master' into docker_in_da_house

Conflicts:
	Gemfile.lock