clear scene un unmount instead of mount

fixes #100

Author: macrozone

ARKit.js

@@ -36,15 +36,14 @@ class ARKit extends Component {
     reason: 0,
     floor: null,
   };
-  componentWillMount() {
-    ARKitManager.clearScene();
-  }
+
   componentDidMount() {
     ARKitManager.resume();
   }
 
   componentWillUnmount() {
     ARKitManager.pause();
+    ARKitManager.clearScene();
   }
 
   render(AR = RCTARKit) {