BREAKING CHANGE:
* refactor(d3-scale) update to major version 2.0. As a breaking change all color related features are removed. schemeCategory20x features are removed without replacement. All other color features are moved to d3-scale-chromatic 1.2
* refactor(d3-scale-chromatic): update to minor version 1.2 by including refactored features dropped from d3-scale 2.0: schemeCategory10 and color interpolators.
* fix(d3-scale) All input arguments for domain or range arrays now also permit ReadonlyArray<T> as inputs. This change allows seamless integration with the color schemes defined in d3-scale-chromatic. This change has been applied to both d3-scale 1.x and 2.x.
* chore(d3-scale-chromatic) activate strictNullChecks
* chore(d3-scale) move d3-scale 1.x into legacy folder `v1` and update tsconfig.json including path mapping for d3-scale itself to pick up legacy version in its own legacy tests
* test(d3-scale) update tests including integration test with d3-scale-chromatic
* test(d3-scale-chromatic) update tests. Including generalized assignment tests for interplators and schemes.
* chore(*) update version numbers for d3-scale and d3-scale-chromatic
