Support multiple classnames

[bananatranada]

I have some reusable utility classes that I'd like to add.

classNames={{
    appear: 'my-appear',
    appearActive: 'my-active-appear a b c', // this does not work
    enter: 'my-enter',
    enterActive: 'my-active-enter',
    exit: 'my-exit',
    exitActive: 'my-active-exit',
}}

[jquense]

done!

[manatarms]

@jquense I need this fix and I was wondering which release this fix was in.
I found this PR #124 (comment)

[manatarms]

Never mind. I found it in v2.2.0
Thanks!