refactoring in computeOutputShape for image resizing layer

Author: dydavidkim

tfjs-layers/src/layers/preprocessing/image_resizing.ts

@@ -68,7 +68,8 @@ export class Resizing extends Layer {
 
   computeOutputShape(inputShape: Shape|Shape[]): Shape|Shape[] {
     inputShape = getExactlyOneShape(inputShape);
-    const numChannels = inputShape.slice(inputShape.length - 1)[0];
+    // inputShape.slice(inputShape.length - 1)[0];
+    const numChannels = inputShape.slice()[2];
     const outputShape = [];
     outputShape.push(this.height);
     outputShape.push(this.width);