Create tag for version 4.2.1

[alert-debug]

As @ruyadorno pointed out in Issue #63, there doesn't appear to be a tag for the specific set of code used to create version 4.2.1 of the dot-prop npm package. That issue has now been closed, so I'm creating this issue to track the remaining small task.

(Of course, it would be really nice if npm/Microsoft performed automated checks on whether a given npm package is verified so that an npm audit would flag this).

[sindresorhus]

Done: https://github.com/sindresorhus/dot-prop/releases/tag/v4.2.1