Animations section image refers to node IDs instead of indices

[javagl]

The Image 7b at https://github.com/KhronosGroup/glTF-Tutorials/blob/main/gltfTutorial/gltfTutorial_007_Animations.md#animation-channels suggests that the animation channel target contains an id property that is a string.

This is a leftover from glTF 1.0 👴 In glTF 2.0, this id was replaced by node, which is an index into the nodes array of the glTF.

The image should be updated accordingly.