.skel is normally the file extension used for binary, but your file is JSON. You should rename it to .json, as some tools assume the file type from the extension.
The HTML you showed uses 4.1 while your skeleton data is from 3.8. The runtime version must match the editor version used to export the data, see:
http://zh.esotericsoftware.com/spine-versioning#%E5%90%8C%E6%AD%A5%E7%89%88%E6%9C%AC
You can change the 4.1 version numbers in your HTML to 3.8.
There is a spine-player for 3.8, but it doesn't have as many features as 4.1. To use 4.1 you would need to export the data again with 4.1. To do that, import your JSON into 3.8, save a .spine project file, then open that with 4.1 and export.
