Add loose-envify dep

[dereklieu]

Here's the missing dependency in package.json.

[timhudson]

This addresses issue #1304

[gaearon]

Is it enough to make it a dev dependency? They are only installed when you run npm install in the project folder. I feel like this should be a regular dep.

[timdorr]

Yeah, it needs to be a regular dep. Check #1306.