api.use nprogress

fixes: Uncaught ReferenceError: NProgress is not defined

Just added the package to a project on Meteor 0.7.0.1 and was seeing this error.
We need to use the nprogress package so that we have the NProgress object

Edit: I could explain a bit clearer, the error is triggered from auto-nprogress.js (specifically line 6) because the package cannot see NProgress unless we define api.use within the package.js :)