Fixed invariant issue when using routers as root element in react classes

Because of the way React does props, it seems like using "this.props.component" is not entirely the best solution for passing in the props.

Luckily, with the way that @STRML structured the function, `component` is scoped in a way that it can be used instead. There's no need for `getDefaultProps` or to use `this.props.component` in this situation.

By using the actual component, rather than using `this.props.component`, we're able to get rid of the invariant issue (see https://github.com/STRML/react-router-component/issues/102 for more details on the issue).