Adds mkdirp which is a missing dependency.

[davidgomes]

When I tried to use the library for the first time I got this error:

Error: Cannot find module 'mkdirp'
    at Function.Module._resolveFilename (module.js:336:15)
    at Function.Module._load (module.js:286:25)
    at Module.require (module.js:365:17)
    at require (module.js:384:17)
    at Object.<anonymous> (/Users/david/src/pentagine.js/node_modules/unminified-webpack-plugin/index.js:6:14)
    at Module._compile (module.js:434:26)
    at Module._extensions..js (module.js:452:10)
    at require.extensions.(anonymous function) (/Users/david/src/pentagine.js/node_modules/babel-core/node_modules/babel-register/lib/node.js:166:7)
    at Object.require.extensions.(anonymous function) [as .js] (/usr/local/lib/node_modules/babel/lib/babel/api/register/node.js:113:7)
    at Module.load (module.js:355:32)

As so, I think you should add mkdirp as a dev dependency.

[davidgomes]

If you think this should be a regular dependency and not a dev-dependency, let me know and I'll fix it 😄

[leftstick]

It's some unused code there, just removed. Thanks for reporting this issue.