rot.js volume step simplify

static/rot/rot.js

@@ -378,16 +378,8 @@
             localStorage.audiomuted = audio.muted = musicmute.checked;
             playMusic();
         })
-        volumeStepDwn.addEventListener('click', () => {
+        volumeStepDwn.addEventListener('click', () => volumeAdd(-0.05))
-            var e = audio.volume - 0.05;
+        volumeStepUp.addEventListener('click', () => volumeAdd(0.05))
-            if (e < 0) e = 0;
-            volumeSet(e);
-        })
-        volumeStepUp.addEventListener('click', () => {
-            var e = audio.volume + 0.05;
-            if (e > 1) e = 1;
-            volumeSet(e);
-        })
 
         updateVolumeLabel();
     }