当我执行“ git push heroku master”时，我得到了
....
Compiled all packs in /tmp/build_6ed6cf9fb377fdab9af8a7b30419650b/public/packs
WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version. Currently, we assume version 2.x when no version is passed. Since this default version will likely change in future versions of Babel, we recommend explicitly setting the core-js version you are using via the `corejs` option.
You should also be sure that the version you pass to the `corejs` option matches the version specified in your `package.json`'s `dependencies` section. If it doesn't, you need to run one of the following commands:
npm install --save core-js@2 npm install --save core-js@3
yarn add core-js@2 yarn add core-js@3
Asset precompilation completed (74.40s)
Cleaning assets
Running: rake assets:clean
rake aborted!
TypeError: no implicit conversion of Hash into String