message: move chroma-js to devdependencies
diff: "@types/styled-system": "5.1.10",
  "@types/styled-system__css": "5.0.14",
  "@types/styled-system__theme-get": "5.0.1",
  - "chroma-js": "2.1.0",
  "classnames": "^2.2.5",
  "polished": "3.5.2",
  "react-is": "16.10.2",
  "babel-plugin-styled-components": "1.10.7",
  "babel-plugin-transform-replace-expressions": "0.2.0",
  "babel-polyfill": "6.26.0",
  + "chroma-js": "2.1.0",
  "concurrently": "5.3.0",
  "cross-env": "7.0.2",
  "enzyme": "3.10.0",
  