v4.0.0

If you are upgrading: please see UPGRADING.md.

Changed

• Upgrade nyc devDependency from ~12.0.2 to ~13.1.0 (@ralphtheninja)
• Upgrade deferred-leveldown dependency from ~4.0.0 to ~5.0.0 (@vweevers)
• Upgrade concat-stream devDependency from ~1.6.0 to ~2.0.0 (@ralphtheninja)
• Upgrade level-iterator-stream dependency from ~3.0.0 to ~4.0.0 (@ralphtheninja)
• Replace remark-cli with hallmark (#621) (@vweevers)
• Upgrade standard devDependency from ^11.0.0 to ^12.0.0 (@ralphtheninja)
• Add .nyc_output/ to .npmignore (@ralphtheninja)

Removed

• Remove IE10 from airtap (#625) (@ralphtheninja)