Compile mac on Travis using correct libetpan

[ralphtheninja]

• [x] Change .travis.yml to only build on mac (currently only linux, which is already handled by Jenkins)
• [x] Run test/integration.js again, it will help us see if the bindings on mac actually work
• [x] Update binding.gyp to use correct /path/to/libetpan.a archive
• [x] Tweak scripts/travis-before-install script to install correct version of libetpan
• [x] .travis.yml should run npm run prebuildify and deploy prebuilt binaries (like Jenkins)
• [x] Release new version of node bindings

[ralphtheninja]

Have a temporary prepatch out and testing it on desktop now.