Update core-js to the latest version 🚀

[greenkeeper[bot]]

The devDependency core-js was updated from 2.6.5 to 3.0.0.

This version is not covered by your current version range.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

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Your Greenkeeper bot :palm_tree:

[greenkeeper[bot]]

• The devDependency core-js was updated from 2.6.5 to 3.0.1.

Update to this version instead 🚀

Release Notes for 3.0.1 - 2019.04.06

• Fixed some cases of work with malformed URI sequences in URLSearchParams, #525
• Added a workaround for a rollup issue, #513