CrawlerLegContact incorrectly refers to Ground (#589)

No game object is named "Platform" therefore the legs never make contact with anything

unity-environment/Assets/ML-Agents/Examples/Crawler/Scripts/CrawlerLegContact.cs

     }
 
     void OnCollisionStay(Collision other){
-        if (other.gameObject.name == "Platform")
+        if (other.gameObject.name == "Ground")
         {
             agent.leg_touching[index] = true;
         }