support running from any directory

For instance, suppose a "theoretical" app called Process uses it through a "theoretical" app called sky-app, but the server process is run from another directory or through something like Forever, leading to something like this:

/opt/skybox/process/node_modules/sky-app/node_modules/requirejs-manifest-builder/builder.js:20
            if(err) throw err;
                          ^
Error: ENOENT, readdir './node_modules/'