The example folder structure defines a rollup.config.json, however the following documentation is for creating a rollup.config.js file. (#1734)

Author: SawyerHopkins

src/v2/cookbook/packaging-sfc-for-npm.md

@@ -50,7 +50,7 @@ For the purposes of this section, assume the following file structure:
 ```
 package.json
 build/
-   rollup.config.json
+   rollup.config.js
 src/
    wrapper.js
    my-component.vue