Add prop for transition duration

[ianengelbrecht]

Nice checkbox. It would be great to have a prop where I could set duration of the transition/animation, in milliseconds. Users might want it to go a bit faster or slower in some cases.

[shanelaw95]

@ianengelbrecht Looks like this got added from a recent pull request. duration can be set as a prop in ms

<Checkbox duration="400" />

[ianengelbrecht]

Thank you!