Fix a npm dependency bug and redirect build files to targetDir

I encountered a couple of problems while using this package. 

Firstly, it doesnt run directly with grunt as npm package is not found. It was working well in atom-starter project as the root build directory has npm installed as a package, but this module doesnt refer to it directly. 

Secondly, the package was not redirecting build files to targetDir despite specifying one. Fixed that too.