correct webpack 2 syntax (#740)
correct webpack 2 syntax (#740)

`System.import()` was dropped in favour of `import()`

See: https://webpack.js.org/guides/migrating/#code-splitting-with-es2015 and webpack/webpack#3098 (PR:; webpack/webpack#3413)
potato4d/jp.vuejs.org,vuejs/jp.vuejs.org,potato4d/jp.vuejs.org,vuejs/jp.vuejs.org