clock: prevent canvas draw smears

Trying to use a transparent background revealed constant
redraws each second -- this commit returns a color
declaration to the background, changing with the media query.

pkg/interface/clock/tile/tile.js

@@ -199,7 +199,7 @@ class Clock extends Component {
       ctr,
       -1,
       2 * Math.PI,
-      'rgba(0,0,0,0)'
+      background
     )
 
     // Day