Update version in `package.json` to 2.1.1 to get it in sync

[simonplend]

2.x releases:

• 2.1.1 - 2020-03-27 - d1f618f
• 2.1.0 - 2020-03-18 - 6024c38
• 2.0.0 - 2019-03-14 - b22c7b7

I have added tags for all of these releases.