v3.0.0

Added

• Add node 10 to Travis (@ralphtheninja)
• Add UPGRADING.md (@ralphtheninja)

Changed

• Update standard to ^11.0.0 (@ralphtheninja)
• Update encoding-down to ~5.0.0 (@ralphtheninja)
• Update leveldown to ^4.0.0 (@ralphtheninja)
• Update levelup to ^3.0.0 (@ralphtheninja)
• Change License & Copyright to License in README (@ralphtheninja)
• Replace const with var for IE10 support (@ralphtheninja)

Removed

• Remove node 4 from Travis (@ralphtheninja)