message: prepare changelog for v3
diff: ## [Unreleased]
  +## [3.0.0] - 2018-01-29
  +
  +### Changed
  +* upgrade to `abstract-leveldown@4` (@ralphtheninja)
  +* upgrade to `prebuild@7` (@ralphtheninja)
  +* changelog rewrite (@ralphtheninja)
  +
  +### Fixed
  +* make sure `destroy()` deletes `LevelDB`-only dir (@joyeecheung)
  +
  ## [2.1.1] - 2017-12-02
  ### Fixed
  :seedling: First release. Extracted from `levelup` as a stand-alone package (@rvagg)
  -[Unreleased]: https://github.com/level/leveldown/compare/v2.1.1...HEAD
  +[Unreleased]: https://github.com/level/leveldown/compare/v3.0.0...HEAD
  +[3.0.0]: https://github.com/level/leveldown/compare/v2.1.1...v3.0.0
  [2.1.1]: https://github.com/level/leveldown/compare/v2.1.0...v2.1.1
  [2.1.0]: https://github.com/level/leveldown/compare/v2.0.2...v2.1.0
  [2.0.2]: https://github.com/level/leveldown/compare/v2.0.1...v2.0.2
  