fixed error in collision bbox code

Author: odestcj

index.html

@@ -497,7 +497,7 @@ <h3>First step: add collision detection</h3>
 <pre><code data-language="javascript">
         // bounding box of robot link in local link coordinates
         robot.links[x].bbox = new THREE.Box3;
-        robot.links[x].bbox = robot.links[x].bbox.setFromPoints(robot.links[robot.base].geom.geometry.vertices);
+        robot.links[x].bbox = robot.links[x].bbox.setFromPoints(robot.links[x].geom.geometry.vertices);
 </code></pre>
 
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