Exclude src directory from npm package

[steelbrain]

To do that we need to add this to .npmignore

src

[developit]

Hi - the src directory is actually intentionally included, because it is referenced as "jsnext:main" for users who want the ES6 source (for things like Webpack 2 / Rollup tree shaking).

[steelbrain]

@developit but if we git ignore we'll get an extremely lightweight package

[steelbrain]

Nevermind the size difference is very small

[developit]

Yup, size diff is about 80k.