v4.0.0

If you are upgrading: please see UPGRADING.md.

Changed

• Upgrade abstract-leveldown from ~5.0.0 to ~6.0.1 (#174) (@vweevers)
• Invoke abstract tests from single function (#174) (@vweevers)
• Use level-concat-iterator and testCommon.factory() in custom tests (#174) (@vweevers)
• Don't use falsy or undefined as not-defined signal (#174) (@vweevers)
  (@vweevers)
• Upgrade standard devDependency from ^11.0.0 to ^12.0.0 (#173) (@ralphtheninja)
• Upgrade airtap devDependency from ^0.0.5 to ^2.0.0 (#161, #163, #168, #172, #177) (@vweevers)
• Tweak copyright years for less maintenance (760b375) (@ralphtheninja)
• Apply common project tweaks (#178, #179) (@vweevers)

Added

• Add nyc and browser code coverage (#169, #180) (@vweevers)
• Add Sauce Labs logo to README (#165) (@ralphtheninja)
• Document that nullish values are now also rejected (#174) (@vweevers)
• Test negative and positive Infinity as keys (#174) (@vweevers)

Removed

• Remove contributors from package.json (80b3e3a) (@ralphtheninja)
• Remove node 9 (0de8721) (@ralphtheninja)
• Remove now irrelevant serialization of nullish values (#174) (@vweevers)
• Remove dummy location from abstract-leveldown constructor call (#174) (@vweevers)
• Remove rimraf devDependency (#174) (@vweevers)

Fixed

• Fix link references in UPGRADING.md for latest remark (f111a6f) (@vweevers)