support node 12.x

[sam-github]

Adds support for node 12.x.

Note: this doesn't break support for anything, I tested all the .travis.yml platforms back to 0.10, and it still works, so this can be published as semver-minor (adds 12.x support, a new feature).

[sam-github]

I tested with sucess on all the platforms, I'm curious to see what travis thinks:

git clean -x -d; nvm i 0.10; npm i && npm test; node --version
git clean -x -d; nvm i 0.12; npm i && npm test; node --version
git clean -x -d; nvm i 4; npm i && npm test; node --version
git clean -x -d; nvm i 5; npm i && npm test; node --version
git clean -x -d; nvm i 6; npm i && npm test; node --version
git clean -x -d; nvm i 8; npm i && npm test; node --version
git clean -x -d; nvm i 10; npm i && npm test; node --version
git clean -x -d; nvm i 11; npm i && npm test; node --version
git clean -x -d; nvm i 12; npm i && npm test; node --version

EDIT: tested on linux

[sam-github]

@msimerson

[msimerson]

fixes #34