message: bump version to 1.19.0 in package.json
diff: {
  "name": "DataFrame",
  - "version": "1.15.0",
  + "version": "1.19.0",
  "homepage": "https://github.com/hosseinmoein/DataFrame",
  "repository": "github:hosseinmoein/DataFrame",
  "author": "Hossein Moein <myseajune@aol.com>",
  