Prevent default on dbltap.

d3.js

@@ -1244,6 +1244,7 @@ d3 = function() {
           var p = touches[0], l = location(touches[0]);
           scaleTo(scale * 2);
           translateTo(p, l);
+          d3_eventPreventDefault();
           dispatch(event_);
         }
         touchtime = now;

src/behavior/zoom.js

@@ -140,6 +140,7 @@ d3.behavior.zoom = function() {
         var p = touches[0], l = location(touches[0]);
         scaleTo(scale * 2);
         translateTo(p, l);
+        d3_eventPreventDefault();
         dispatch(event_);
       }
       touchtime = now;