FIX: Make tracklist URI's work again

With the latest changes in Mopidy 1.0, the manipulation of the tracklist
controller requires a list of URI strings instead of a single URI.

This is all described here:
https://docs.mopidy.com/en/latest/api/core/#manipulating

This change should make the tracklist action work again.

mopidy_pummeluff/actions.py

@@ -25,7 +25,7 @@ def replace_tracklist(core, uri):
     '''
     LOGGER.info('Replacing tracklist with URI "%s"', uri)
     core.tracklist.clear()
-    core.tracklist.add(uri=uri)
+    core.tracklist.add(uris=[uri])
     core.playback.play()