babel-preset-gatsby-package doesnt specify corejs in babel preset

[baerrach]

Description

While trying to develop a Gatsby plugin I get the following errors

WARNING: We noticed you're using the `useBuiltIns` option without declaring a core-js version.

This is because babel-preset-gatsby-package does not specify corejs in the preset

https://github.com/gatsbyjs/gatsby/blob/c5cc361d26b2e9e0b31ec68e9f040d7d97c4572f/packages/babel-preset-gatsby-package/index.js

But babel-preset-gatsby does.

https://github.com/gatsbyjs/gatsby/blob/c5cc361d26b2e9e0b31ec68e9f040d7d97c4572f/packages/babel-preset-gatsby/src/index.js