Fix ripple directive for lit-html 0.13

[balloob]

In 144213a packages got dependencies updated for lit-html 0.13. However, there was a breaking change in lit-html 0.13 that was not taken into account:

• [Breaking] Directives are now defined by passing the entire directive factory function to directive(). (Change directive() function to wrap the entire directive factory. lit/lit#562)

This PR will update the Ripple directive to use the new format.

CC @azakus

[straversi]

Thanks for fixing this!