Missing `"files"` in package.json

[jdthorpe]

If you use yarn to install this package from github by adding like so:

//package.json
{
   ...
   "dependencies":{
        "react-chatbot-kit": "git+https://github.com/FredrikOseberg/react-chatbot-kit.git"
    }
}

and then installing with yarn, the build/main.css file is excluded from the install. (This isn't an issue when installing with npm, but technically yarn is behaving to the spec and not npm). The solution is to add a "files" attribute to the package.json of this package.

{
  "name": "react-chatbot-kit",
  "files": [
    "build/*.css"
  ],
}