Slim down NPM package

[avaly]

This PR slims down the NPM package. See http://blog.npmjs.org/post/165769683050/publishing-what-you-mean-to-publish for reasoning.

$ npm pack
i18next-scanner-2.0.0.tgz

$ tar tvf i18next-scanner-2.0.0.tgz 
-rw-rw-r-- 1000/1000      1797 2017-10-15 13:32 package/package.json
-rw-rw-r-- 1000/1000     17235 2017-10-15 13:30 package/README.md
-rw-rw-r-- 1000/1000      1082 2017-10-15 13:30 package/LICENSE
-rw-rw-r-- 1000/1000       492 2017-10-15 13:32 package/lib/ensure-array.js
-rw-rw-r-- 1000/1000      3368 2017-10-15 13:32 package/lib/index.js
-rw-rw-r-- 1000/1000      2143 2017-10-15 13:32 package/lib/jsx-parser.js
-rw-rw-r-- 1000/1000     30445 2017-10-15 13:32 package/lib/parser.js
-rw-rw-r-- 1000/1000       709 2017-10-15 13:30 package/tasks/index.js

[coveralls]

Coverage remained the same at 92.683% when pulling 03c95af on avaly:feature/slim-npm-package into c750f57 on i18next:master.