Support React 16

[zhangjunah]

When I set my package.json like this:

"dependencies": {
  "react-dom": "^16.0.0",
  "react": "^16.0.0",
  "react-toastr": "^2.9.3"
}

Then I run npm i, the node_modules/react-toastr/node_modules/react-dom is installed, this means npm install a react-dom 15.6 for react-toastr. So, when I run my app, it is crashed, but if I remove the dir node_modules/react-toastr/node_modules/, everything runs well.

I hope you to publish a new version to support React 16, in fact, I think all the code runs well on React 16, only need to change the package.json

[mclapa]

@zhangjunah might explain this error I'm getting

Element ref was specified as a string (toasts__0) but no owner was set. You may have multiple copies of React loaded.

[whns]

Is this still happening with version 2.9.5?