Prevent npm install from picking up existing node_modules dirs

Currently meteor bundle will break if there exists a node_modules folder anywhere in a folder above the app dir.

This is due to the fact that if npm sees an existing node_modules folder in the current directory OR higher up in the folder tree, it will choose to install into it. (See https://npmjs.org/doc/folders.html under "More Information").

This fix creates a node_modules directly after creating the .npm folder so that npm install will work as expected.