Updated to use prop-types and create-react-class

[lucbelliveau]

Fixes #17
Removed deprecated proptypes and React.createClass

[anishaas]

@lucbelliveau Thank you for providing this fix. Did you manually add this edited code as a dependency to your project?

[lucbelliveau]

@anishaas You can add git branches as dependencies... like this:

{
  "dependencies": {
    "react-packery-component": "git+https://github.com/eiriklv/react-packery-component.git#fb2a7cf"
  }
}

[jakedowns]

using
"react-packery-component": "git+https://github.com/lucbelliveau/react-packery-component.git#3458fdcfe95b02186fae75ed4c9a22e53b745233" on our project

any chance this will get merged?