v5.15.0

Changes from v5.14.0:

monorepo

• Update dependencies, including use of D3 v6 packages.
• Refactor all packages for JavaScript modernization. (thanks @domoritz & @lgrammel!)

vega

• Update vega-core build to use D3 v6.

vega-scale

• Add turbo and cividis color palettes. (thanks @mcnuttandrew!)