Updated CircleGeometry to the new instancing pattern.

src/extras/geometries/CircleGeometry.js

@@ -50,5 +50,4 @@ THREE.CircleGeometry = function ( radius, segments, thetaStart, thetaLength ) {
 
 };
 
-THREE.CircleGeometry.prototype = new THREE.Geometry();
-THREE.CircleGeometry.prototype.constructor = THREE.CircleGeometry;
\ No newline at end of file
+THREE.CircleGeometry.prototype = Object.create( THREE.Geometry.prototype );