Defer style prefixing until componentDidMount

[bvaughn]

Server-side rendering logs the following warning:

Either the global navigator was undefined or an invalid userAgent was provided. Using a valid userAgent? Please let us know and create an issue at https://github.com/rofrischmann/inline-style-prefixer/issues

This is because we're prefixing the initial styles in the constructor rather at which point we may be in a server-side rendering context. We should probably move this prefixing operation to componentDidMount to ensure that we're in a browser context.

This will require a re-render but that's probably acceptable.