It says: "Couldn't load pack metadata" and "MalformedJsonException". This makes me think that there is a syntax error in your pack.mcmeta file. make sure it looks something like this:
"description": "Testing 1.13 datapack"
I don't know which number you have to use in the pack_format, but it should be a number between 1 and 3. You'd have to play around with that. This is an exact copy of the pack.mcmeta file in my own data pack, and it worked for me.
Also make sure that it is loaded by using the /reload command. If your loot table is incorrect, you should get an error message.
It seems like your folder structure isn't quite right.
The minecraft wiki has a page about data packs, which tells you what your folder structure should look like.