transitions for hover states on cirlces

public/css/app.css

@@ -1,3 +1,12 @@
 svg {
 	border:1px solid black;
 }
+circle {
+	r: 5;
+	fill:black;
+	transition: r linear 0.25s, fill linear 0.25s;
+}
+circle:hover {
+	r: 20;
+	fill:blue;
+}

public/js/app.js

@@ -27,7 +27,6 @@ var render = function(){
 		});
 		circles.enter()
 			.append('circle')
-			.attr('r', 5)
 			.attr('cy', function(datum, index){
 				return convertYDataPointToVisualPoint(datum.distance);
 			})