Remove the dev folders in the build

Hey Paul,

Firstly, massive props for shipping 3.4 :+1: Great work as always from you!

I saw you popping in Grunt when I woke up this morning and was keen to see where you were at with it. This patch will fix up point number 2 here: https://github.com/paulgibbs/achievements/issues/116

I'm also curious to know how you've got the new folder structure setup on your computer. Have you got a symlink to the src folder in plugins/achievements?

It looks like you could use some watches in Grunt for this as well so I might have a play around now for you to see if I can come up with anything. I've only been using Grunt for about 14 days so I'm a noob too. I've been playing around with a Sennza version of 10up's grunt plugin: https://github.com/sennza/grunt-wp-plugin :grin: