Update package-lock.json to lockfileVersion 2

[cpcallen]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide

The details

Proposed Changes

Update package-lock.json from lockfileVersion: 1 to lockfileVersion: 2.

Reason for Changes

Version 7 of npm does this automatically; as a consequence, most of the team are using npm v6 to avoid this update. But I believe the update is harmless:

• lockfileVersion: 2 is backward-compatible with lockfileVersion: 1, so npm v6 can work fine with new file (although it does print a warning, because it can't know that this file-format-from-the-futrure is fine).
• npm v7 is backwards compatible as far as node.js v10, so this update does not prevent anyone from using npm v7 with any of the older versions of node.js we wish to continue supporting.

Test Coverage

Awaiting CI tests on GitHub.

Additional Information

You can update npm to the latest (v7.x) by running npm install -g npm.

[maribethb]

Thanks for the explanation of why this is safe! We should probably do this for all of blockly-samples as well.