Use changedTouches instead of touches.

This is because the "touchend" event removes the touch from
event.touches on iOS, but it can still be accessed via
event.changedTouches.

d3.js

@@ -3530,7 +3530,7 @@ function d3_svg_mousePoint(container, e) {
   return [point.x, point.y];
 };
 d3.svg.touches = function(container) {
-  var touches = d3.event.touches;
+  var touches = d3.event.changedTouches;
   return touches ? d3_array(touches).map(function(touch) {
     var point = d3_svg_mousePoint(container, touch);
     point.identifier = touch.identifier;

src/svg/touches.js

@@ -1,5 +1,5 @@
 d3.svg.touches = function(container) {
-  var touches = d3.event.touches;
+  var touches = d3.event.changedTouches;
   return touches ? d3_array(touches).map(function(touch) {
     var point = d3_svg_mousePoint(container, touch);
     point.identifier = touch.identifier;