Clean npm package

[ai]

@tallesl thanks for package, I used it in my project.

The only problem with it, it brings tests files to my node_modules. They are small, but if every dependency will bring tests files, node_modules could be increased 2x :).

So this small PR cleans npm package from test files. Your can release it as patch version, since it doesn’t have any affects to your API.

[coveralls]

Coverage remained the same at 100.0% when pulling eb232b1 on ai:patch-1 into 1dd63f0 on tallesl:master.