在vue文件中，要引入相应的样式，经常会用到
@import "~common/stylus/mixin"这种写法，为什么会用到~？查看了stylus-loader文档，发现这句话

 It also lets you load a stylus file from a package installed in node_modules or if you add a modulesDirectories, like modulesDirectories: ['node_modules', 'web_modules', 'bower_components'] option you could load from a folder like bower_components. To load files from a relative path leave off the ~ and @import 'relative-styles/my-styles'; it.

结合本人做的测试，发现这个~和webpack配置文件中alias有关，只有在webpack配置文件中配置了alias，设置了相应的别名路径，@import才能通过~别名来实现查找相应的文件。