add .npmignore
During npm publish, certain files and directories can be ignored
from the package.
See https://npmjs.org/doc/developers.html#Keeping-files-out-of-your-package.
This reduces the package size.
Keeping AUTHORS, CHANGELOG, CONTRIBUTING.md, LICENSE-MIT
Ignoring docs, test, .editorconfig, .gitattributes, .jshintrc,
.travis.yml, Gruntfile.js
Merge pull request #209 from CaryLandholt/npmignore

add .npmignore