webpackimportstylus时被当做一个dependency,如何解决

import  'assets/stylus/index.styl';

 ERROR  Failed to compile with 1 errors                                                                                                                            

 This dependency was not found:

* assets/stylus/index.styl in ./src/main.js

To install it, you can run: npm install --save assets/stylus/index.styl