Fix issue #35, made _chain check typeof X === 'undefined' rather than X === 'undefined'

[SimplyLinn]

Also made Gruntfile use the FS module to look for the correct placement for jsdoc-thing. It failed on my system using NPM 4.

[krampstudio]

That's really great! Thank you. For the jsdoc, I'll discard your changes and only update the version of grunt-jsdoc (which I'm also the author) to support npm 4+